Why did Millions of Sea crows gathered together at the beach of Ras AL Khaima?

The Live video links to YouTube for the Incident happened is given below:

Why did this happen?

This is one of the reasons for the gathering of crows,explained at reference.com

Often the crows will gather in large groups before making it to their roosting spot. Once the nighttime settles in, the group makes their way to a safe spot to sleep. The process is not always peaceful, however, as the crows sometimes fight one another. Large groups of crows are more often seen in winter and fall months as during the breeding season, the crows tend to stray off on their own to built suitable nests. During breeding seasons, crows are territorial of their nests, but these are abandoned as the weather begins turning cold. Sometimes, crows will also group up if they feel threatened or an abundance of food is found in one spot such as large fields of vegetation.

While some species of crows migrate, the majority stay put all year long. Crows are found all through the United States, and only have a life span of under one year on average. The majority will die before hatching or as nestlings. Crows only breed one time per year and average three to four eggs at one time. The entire process takes nearly four months since the eggs incubate for 20 days and will not hatch for another 35 days.

https://www.reference.com/pets-animals/crows-gather-4ab7cb53a083589b

Why do crows congregate in large numbers to sleep?

One of the great animal phenomena of the world is the congregation of large numbers of birds into a single group to sleep together. Such communal sleeping groups are known as "roosts." Many species roost in groups; such things as crows, robins, starlings, blackbirds, swallows, and herons. Most do this only outside of the breeding season. Some species, like starlings, also forage together in great numbers. Others, such as herons, disperse out from these gathering areas to forage singly. For crows, roosts are primarily a fall and winter thing. Numbers peak in winter and then decrease near the beginning of the breeding season (usually in March). It appears that all crows will join winter roosts, even territorial breeding crows. Most breeding crows sleep on their territories during the breeding season, but join the roosts afterward.

Why have these roosts recently moved into cities?

A number of possible explanations exist for the relatively recent influx of roosting crows into urban areas. The birds are not making drastic shifts in behavior; crows have been gathering into winter roosts for as long as there have been crows. We know, for example, from work done in the 1930's by John Emlen at Cornell University that approximately 25,000 crows were gathering in a roost near Auburn, NY in the winter of 1932-33, and that a large roost was present in 1911-12 (Emlen, J. T., Jr., 1938, Midwinter distribution of the American Crow in New York State, Ecology 19: 264-275). The big difference is that they were roosting 3 miles south of town then and are roosting smack in downtown Auburn today. Any increase in size of the roost would be imperceptible, compared to the change of locale.
A couple of things may have worked together to get crows into town (both for nesting and roosting):
1) The 1972 extension of the Federal Migratory Bird Treaty Act of 1918 to cover crows. At this point the hunting of crows became regulated. No longer could anyone anywhere take shots at crows, but had to do so (theoretically) within proscribed guidelines and hunting seasons. It is possible that this change may have resulted in the decrease of shooting pressure on crows, allowing them to become more tolerant of the presence of people.
2) A prohibition on the discharge of firearms within city/village limits. It is conceivable that crows somehow stumbled across the fact that they could not be shot in cities because of local ordinances against shooting in town. So, in fact crows might have somehow figured out that the best thing to do to live with their enemy was to get as close as possible, not stay away. Many crow hunters do most of their hunting along flight lines of crows moving to roost. These flight lines through urban areas are protected, those in rural areas are not.
Once crows overcame the urban barrier, a number of possible advantages could extend to them:
a) Cities are warmer than rural areas. In most places a difference of 5-10 degrees F exists, sometimes referred to as a "heat bubble" over cities. Because roosting is a winter phenomenon, warmer spots could be important.
b) Great Horned Owl (Bubo virginianus) populations should be lower in urban areas. Next to people with guns, Great Horned Owls pose the largest danger to an adult crow. Great Horned Owls take adults as well as nestling crows with great regularity. (That is why crows hate them so much!) Owls probably are regular attendants at crow roosts, as owls wake up as the crows are heading into the roosts, and sleeping crows should be pretty easy picking.
c) Artificial light assist crows in watching for owls. I have noticed that many urban crow roosts are not located in nice dense trees where the crows would have microclimate advantages, such as protection from wind or cold. Rather, the crows perch out on the tips of bare branches of leafless deciduous trees. I was quite surprised by this at first, but then I noticed that many (most?) roosts are located near sources of bright illumination, such as streetlights and parking lot lights, like the lights at the Auburn prison and Syracuse University. It makes sense for crows to like "nightlights" to protect them from their biggest bogeyman, the Great Horned Owl. Crows don't see well at night; owls do. Crows near street light could see approaching owls. Also, if a crow gets scared out of its roost in the middle of the night (presumably by an owl taking crows), in lighted urban areas the crows can see where the predator is, and perhaps more importantly, can see to find another perch. You can imagine that flying blindly into the dark is not something any bird would choose to do. I was surprised at the amount of activity at the Auburn roost well after dark. The crows were still making a lot of noise and even flying from tree to tree. In other roosts I have watched that were in darker locations the crows quieted down rather quickly and no movements between trees were seen shortly after complete darkness.
d) Urban areas provide large trees for roosts. In many places some of the largest trees to be found are in urban areas. Many trees in parks and cemeteries were protected from the severe logging of the end of the last century, and are some of the oldest trees around. These large trees may be especially attractive to crows.

 
source: http://www.birds.cornell.edu/crows/crowfaq.htm 

Many says this as the Sign for a natural disaster to come. Nature shows such signs before those disasters. May be any earthquakes,Volcanic eruptions of Heavy winds. Lets hope,this is just what explained above. More explanation will be there. Stay tuned.