Actually it wouldn't in this case where a squirrel had chewed through the casing of the wire, but thanks for playing.
If there was an overload the ocpd would protect the circuit wiring. That is what it does. If the ocpd did not trip, either there was no overload or the ocpd was defective. A short circuit is not an overload. It may create a high current flow situation but a short circuit by definition is irrelevant of amount of current flow. You can have a high current flow short circuit or you could have a low current flow short circuit. It all depends on the resistance (ohm value) of the short circuit.
An ocpd is not designed to do anythng in a low current short circuit. If the short circuit creates a high current situation (behind the ocpd designed capacity) it would have tripped but it is not based on it being a short circuit but an overload.
The electric heater is meaningless. In fact, given the cause of the fire was a short circuit, in some situations it could have happened with absolutely no load on the circuit.
Now there is another possibility where there was neither a short circuit or an overload that could have caused a fire. If the conductor (wire) was damaged to where it caused the cross section of the wire (circular mils) to be small enough that a normal load caused enough current flow for that damaged part of the wire to not be able to carry a normal load without overheating; That could cause enough heat to start a fire where there was neither a short circuit or an overload (of the circuit design).
Thanks for playing but when you wish to attempt to educate an electrician about electrical circuits; well, let's just say you are out of your league.