Pure speculation, but looking at the videos, and considering the fact that it was at the high-G end of the bottom of the loop, and there was no attempt to eject, I'd speculate that the pilot suffered GLOC (ie. Blacked Out) and went into the drink.
Whatever the actual cause turns out to be, it's sad news -- R.I.P. -- condolences to friends and family of the pilot.
Regards,
4 <S!>