Sure seems like a object caused the penetration. It could be flexing but has to be a object or corner that did that penetration. The curled edges seem to be more than a crack.
Edit: I take it back about penetration, better pics later in the thread show what I at first thought were curled in edges are in fact part of the bed rib end and already curl in. Stress crack, seen the same thing when thin bottom boats are carried on roller bunks on trailers. Unless the roller is mounted right under a cross member you get cracks over time.