Strange one - looking at the spray he was into wind - so Vortex Ring or Settling with Power unlikely.
Looks like a power loss of some kind. If so they did a good job on the ditching- flare, level, cushion - splash.
Glad everybody got out and no rotor parts broke off and headed for the beach.
Gotta say the people in the water were swimming to the rescue in quick time - good on them!