wwaswas – ok, you have the good grace to stop digging 😉 You’re underlying sentiment may well be correct, but I’m struggling with the pseudo-science of the argument… and here isn’t the place to go through a degree course of material science and solid mechanics to get to the bottom of why.
FWIW, looks to me like a fatigue failure a well. The fact that the OP is a skinny runt (…none taken…) would tend to support fatigue cracking, rather than bending (yielding of the material) from taking a big hit under the backside of someone of larger proportions.
A few lines of history and a couple of pics is far from conclusive either way though, so the pitchfork stays in the barn 😉