You assume everything is in good working order. Perhaps it was. Is this the type of vehicle that is designed for offroad abuse? Is this the type of owner that would do that anyways? Was there a secondary malfunction or perhaps something caught in the area before or after the accident that contributed to the cause?

Brakes get hot. Hot enough to burn you pretty good even on a car that hasn't been to the track and maybe even hot enough to light organic debris that comes in contact with it on fire. Which is probably pretty difficult normally but might be a lot easier if you bash a bunch of that structure to bits in a high speed accident.

Real mystery though.