I believe the shape of the vessel matters more than the size of the engine, especially in the water and the faster you go.
That said, this video looked funny but at least weird (if not fake): why choose a fixie (single low gear) bike instead of a normal bike? It's also dangerous, in the road downhill without brakes. Also the girl on the scooter was ready with a switched on camera on her legs to take a picture on the fly. I mean, the whole thing didn't look so real.
But in the end it's like you say: even if he initially is under engine braking, while he overtakes the others nobody is under engine braking (the other bikes are not "constrainted") and the only difference is the shape of the vessel.