no way that happen just by getting hot.
aluminum has a melt point of 1200F....so to get it soft enough to warp like that with no other interference, i would think it would at least have to get to 1/4 of that temp. i doubt it got 300F.
I would take it back and try talking to someone else. The guy I talked to was under 30 I would say so maybe that had something to do with it.
looks like you pressed down on it or something. it didn't just happen from heat.