that is the what appears to of happened yes. frame has no cracks, as far as i can tell there was no damage to it, i hadnt fallen off of it recently either.
i imagine there was a manufacturing defect in there somewhere though, or it had fatigued over time.
Just so I have this right - you bent your rear triangle completely out of shape by pedalling too hard?
@h2o seems to suggest prior damage and I'd agree.