I'm not trying to be antagonistic or anything here, and as a total newbie I may be talking out of turn... BUT...
Erm, is it just me? or is there a serious flaw in this test procedure. First of all, jumping into a swimming pool with an approximation of weight made of bricks will not give you anywhere near realistic characteristics, especially without the added loads/forces of a wing.
Also, any body of open water is subject to forces far beyond those that can be simulated in even the largest of swimmimg pools. Crosswinds, tidal flow, undertow/swells, waves etc etc etc.
As for the wing, the report says it was seen to be still flying at first. At the base of the cliffs it's anyone's guess what that was doing in the various vortices that always occur. (A VERY painful, but thankfully brief unexpected flight happened to me when I launched a 4sqM parafoil kite too close to rocks on Dartmoor in only a 15knott wind a few weeks ago!) Once it gets waterlogged and therefore then subject to the law of sod AND Posiedon,, it doesn't bear thinking about.