At that height and that weight, the surface tension of the water and the size of the object, it would be more of a slap than a splash. Sounds real to me.

Just to elaborate on Freds answer: Water is practically non-compressable, and if you were to jump from that distance, you'd be crushed when you hit the water. It's more or less the same thing with the rock; Instead of softly displacing and pushing the water aside, it slams into the surface as if it was concrete. The water simply doesn't have time to get out of the way of the rock at first. The splash is still there though, and if the microphone was close enough you'd be able to hear it, but at this distance you only hear the loud crack of the initial impact.

Definitely real, you can clearly hear the echoes and reverb from the canyon. The delay is also accurate, if someone has faked this, they clearly understand physics.