Ive actually seen quite a few bows do that and never have seen a bent cam...

I would say that your brother might not of even dry fired the bow, he just probably torqued the string pretty good with his fingers when letting down and it ran of track...

It sounds just like a dry fire but its a little less intense

Id do just as big country said though and take it somewhere and ask them to check it all out... It will probably cost you a little money to have the labor done, but likely you will have nothing at all wrong or just bent axles which are an easy fix...

If you let it go by and dont worry about it, those axles may come back to haunt you when your trying to tune etc...

Hoyt used to have a big problem with factory axles not being straight and tuning doing in depth tuning with them was work...