What happens to the pressure inside of a fixed volume (such as a refrigerator), when temperature increases? What if the gaskets did not seal the door adequately and there was some air leakage? Could there have been more heat damage than flame damage? Could the fire have smoldered inside the refrigerator creating enough heat to degrade the gasket allowing air to leak in and support brief flaring of flaming combustion (which produces more smoke, chokes the fire, which smolders until the process repeats?) [Could a Martian ray beam have started the fire?]

Impossible is probably a bad word to use, except that testifying in courts teaches you that juries (judges and lawyers, too) love absolute certainty in their witnesses. Impossible is pretty certain.

Steve