Why would anyone jump on a prop??
When I was a senior in high school...my cousin did something like this. He was drinking and fell off the boat...then got tangled up with the propeller. Another guy from a second boat ended up saving him. He had a huge gash across his head and it a good seven inch type cut.
If the prop was turning the boat was moving even if it was sinking. Ever try to out swim even a slow moving sail boat? You'll be surprised how fast they move when you're in the water. My guess is the boat ran over him.
If he had any training in water craft safety he would have shut down the engine before abandoning ship, in fact, almost ALWAYS the best course of action is to stay with the vessel. Small vessels are designed not to sink.
Avast there mate!
"There are divers over the side, do not rotate screws, cycle rudders, take suction from or discharge to the sea or operate any underwater equipment without first contacting the Chief Engineer and the diving supervisor."