If it was just a single engine failure he would have sat there on the water fat dumb and not so happy whilst the good engine kept everything turning enough for him not to turn turtle
And then what? Not enough power to get airborne again and God knows what shock loading to the transmission from TR impact with the water.
A water landing in an aircraft designed for it (done it in a Sea King) is exciting enough and you need a boat shaped hull to manage a SEWTO unless you have a ridiculous amount of power available on the remaining engine. If you are still attached to a water bucket this will be impossible.
On water entry without sponsons or flotation gear you are going to roll inverted regardless.
A driveshaft failure would have produced a lot of yaw - of which there is none in the video - and a harder impact.
If it's not a single engine failure/ rundown/freewheel failure I'll be very surprised.