IMHO, it a very well done fake.
Only fails at basically one point I can pick. Its impact with the water is wrong.
When the 'spaceship' dives into the water,
1> the splash 'shape' is wrong for something hitting the water that rapidly.
2> the sound of the splash is instant, no time delay as one would expect from an object 300-500 meters distant.
3> the splash sound is too 'soft', not the 'slap' sound of a solid object hitting water.

But it is certainly one of the better ones Ive seen.