You all are thinking too narrowly. The theory is saying the nose wheel tire was the "initial" source of the problem. Overheat due to exceeding tire speed limit on the takeoff roll or any other numerous causes.
The exploding tire OR tire on fire, who knows who cares, can and has created damage to critical components in the E and E bay. Any one of those damaged components then can cause shutdown of that component or others. And from that damage IS the source of the smoke or fire.
Lots of things can cause an electrical fire, electrical fire is on my list (way down). But I don't think that was it. Too many sensors to allow damage to go otherwise undetected in this particular case, as I said.