Having flown sea planes in warm climates in the past I am not at all surprised that this accident happened. You can actually see corrosion forming in front of your eyes if you look hard enough. My speculation is spar failure but we will leave it up to the experts. A few guys I flew with really liked to chuck the airplane around ie pulling a few G's, and my reaction was you can do it but with me watching from the dock.
This is truly a sad event for all involved.