” Even true for vessels that don’t have built in flotation.
There’s been many cases where a ship was abandoned at sea during a storm, only to be found still afloat after the storm had passed, surviving the storm on its own.
As for the fellow who jumped, unless there’s something the story omitted (e.g. boat might have been capsizing while under weigh, as when turning too sharply for the speed, and he tried to jump clear), he probably just panicked.”
That could be the reason he jumped and the boat was moving under him.
A tight turn at too high a speed can be pilot error.
But it could also be from steering malfunction.
Years ago, large outboard motors that were controlled with a steering wheel instead of a tiller, worked by a system of cables on pulleys between the wheel and the motor.
When a cable snapped, the engine was free and there was nothing to prevent the propeller from walking the outboard sideways, immediately putting the boat into a vicious turn if at high speed.
If the boat were going over that fast, you’re probably better off jumping than having the boat land on top of you and knocking you out.
Trapped underneath the boat and unconscious, would seriously reduce your chance of survival.
There might still be some old boats with steering like I’ve described.
I assume modern steering systems have safeguards against this happening—but I guess can always happen (as when the bolt securing the steering gear to the motor fails).