If there was a brake fire, it may have been caused by low air pressure which would apply the brakes with excess heat. Detroit engines are known to be oil leakers without adequate maintenance. That would increase the possibility of a fire.
Possibly. The vehicle was in very slow moving traffic. My gut feeling it wasn't brake. I say this because if it were, it would take time, and the heat would have been intense, and the driver would have most likely smelled it long before it actually ignited, since it was in slow moving traffic. Just speculating here.