This was most likely an arcing fault and would never pull enough current to open a breaker. The fire may have been prevented by an AFCI depending on the type of arcing that produced the heat. It sounds like a poor quaility connection on the receptacle that was producing heat when there was a load. If so this wa a series arcing fault and even an AFCI might not detect this fault. If it was an arc between the hot and grounded conductor, that would be a parallel arc, and an AFCI would have opened the circuit.
