If the bicycle were allowed to sit outside in an environment where freezing temperatures are normal, at certain times of the year, water that finds it way inside of a bicycle frame will freeze. The water expands when freezing and with powerful force. I have seen my share of chain stays mushroomed out to the point where the tubing actually split.

Look elsewhere on the frame for bulging. Usually, the ice thing is most noticeable on the underside of the chain stays.

I am not saying that that is the case, in this instance, but it is one possibility. To that possibility, add this...

You might have better luck finding answers, if you show a big picture of the bicycle, so that we can see the profile. Crash damage can sometimes be determined by looking directly at the side of the bicycle.