I am not sure this is about VRS. Once airspeed is below 30 kts, with a high rate of descent, there was simply not enough power to overcome the inertia before the sea got in the way. VRS takes time to develop. This is low speed, height ROD condition. Similar to descending downwind.
As HC says, the actual mechanism is just to result of the initial problem. Failure to maintain airspeed whilst descending.
DB