From that posted video of the crash, it appears that the plane may have hit the surface of the water for some distance before striking the retaining wall. There is a white streak which looks like spray before the orange/brown dust cloud.
If the plane had hit the water, wouldn't the immediate effect have been to slam the nose down? It's possible the white streak was a result of the engine thrust on the surface of the water. But the white streak seems to go for quite a distance; well past the 747 on the taxiway, which would suggest it's simply dust, as opposed to the orange/brown smoke plume.