Any laminated, cored composite piece would have it's skin crushed if it had been to any great ocean depth.
Composites float very nicely and do so pretty much indefinitely. The whole point of the various cores used with composites is that they separate the two skins and do not absorb much of the resin used during manufacture. This tends to make them quite waterproof. It also makes them susceptible to crushing under pressure.
Did the piece float up from the ocean depths? No way.
Pieces like this respond much more to prevailing winds and breaking waves than currents, and with several cyclones having passed through the central and northern Indian ocean since MH 370 was lost, it could've come from a very broad area.