looking at all the sharks in several diagrams — considering the size, stoutness & coloration (I can't see distinct markings) I think it's likely a lemon shark — which probably woulda done little more than check him out with a small chance of taking a nip. It's definitely not a shark that woulda maimed him on a single attack — or pulled him under. Even those "maneater" smaller reef sharks don't do that. They just nip you to death — turning you eventually into the main course of a feeding frenzy.

He really shoulda gone for the flotation ring, regardless. I agree w commentators that the shark might've spooked him away from the ring & he didn't realize how small a window he had to grab it. Poor kid.