Clearly, the cooked wiring got between the outside rails and the center rail, so your analysis is probably as good as any. Without examining the unit personally, no way of really determining if the analysis is correct.
FWIW, I've seen this many times with passenger cars that have derailed and one pickup roller landed on an outside rail. I've seen it in a couple of diesels that have done the same thing. K-Line was notorious for running power through the motherboard PCB traces for the front and rear trucks, frequently that trace would be smoked by a derailment. Not that hard to fix, just annoying.
