I've had my Stang for about 2 years now. One time while underneath I noticed the entire passenger floorboard had a HUGE gaping hole in it with a new piece of sheetmetal bolted in.
Turns out the RH exhaust fell off and ripped through the floorboard. I don't know any details beyond that, but it sounds strange unless he was driving real fast in reverse or something....
I say treat yourself to a new exhaust
Good luck,
Rich D.