When deployed on the Tarawa (LHA-1) in the early 80’s we had a man blown overboard by a Harrier...about half way between the Philippines and Australia.
That’s an enormous body of empty ocean. And it was by no means “smooth as glass”.
The good news is he was wearing a vest.
The bad news is they sent a CH-53 to pick him up. The downward thrust was so severe it pushed him under and he drowned.
I was one to the pilots on a 6 bird flight from NC to Homestead, FL to Grand Turk to Roosevelt Roads, PR back about 1978. We knew back then that we did not have "Self Rescue" capability, due to the extreme rotor wash, so we had an Air Force C-130 with rescue jumpers fly along as escort.
In the case you mentioned, the rotor wash probably did not push him under, rather the intensity of spray driven by the rotor wash made it impossible for him to breathe.
When refueling at civilian airports we had to be very careful not to hover near other aircraft. Folks get a mite testy when you blow all those Cessnas, Pipers & Beechcraft into a heap.