Yes, I think the pilot has to have deliberately done it. The turns after the transponder went off are too intentional, and nothing like the flight plan the plane was meant to be flying.

I saw a simulation that looked fairly convincing, that showed if the plane was ditched in a controlled glide from where the last ping was received, assuming that's were it ran out of fuel, then the plane would have glided out of the area that was searched. They also claimed that the damage on the flaperons and other control surfaces that washed up was fairly consistent with landing fairly level, where those control surfaces may have been ripped off but most of the rest of the plane might have been fairly intact and would have quickly sunk in mostly one piece. It seemed fairly plausible.