Very strange indeed. In the pics it looks as if the wing spar was intact (I am, however, not an aircraft mechanic, I only fly the things), so at least going on what we see here it doesn't look like a spar failure. Also, a pilot flying just a few minutes behind the accident a/c mentions 'light winds' and nothing about severe turbulence. Without wanting to jump to conclusions, Voel may be on to something
Btw, Voel, how's the sandpit going?