Could also be caused by the owner hooking something up the 12V system which failed. This cannot be emphasised more: always fuse anything attached to the 12V system, like on any car. And use an automotive safe fuse (like Littelfuse ATOF.) However, unlike an ordinary car, substantial continuous current is available from these points with the ignition OFF with minimal risk of draining any battery, which seems to encourage continuous connection setups. I have seen some people tie into the 12V "jump start" points in the front of the vehicle. These are probably unfused and can provide over 150 amps continuous, with many more supplied by the 12V battery. (I presume the battery is wired in parallel with the DC/DC converter. If it is arranged in a pass-through fashion, it might be fused.)
When you dump 150 amps into thin wiring going to some lighting or camera accessory, you melt stuff, and the front of the vehicle has a lot of plastic which can burn. Boom, you've got a fire.