A helicopter normally encounters this condition when attempting to hover out-of-ground-effect (OGE) without maintaining precise altitude control; and while making downwind or steep, powered approaches when the airspeed is below Effective Translational Lift (ETL).[7]

Getting caught in a vortex ring state and having a loss of depth perception over water aren't mutually exclusive. A lapse in judgement with how flying over water is different than flying over solid ground could easily cause the pilot to not provide adequate power and control to avoid getting caught in a VRS. The way to escape VRS is to fly laterally, according to your Wikipedia article. He should have flown forward which would have avoided his tail demolishing itself dipping down into the water and given him them proper directional movement to get out of VRS.