Is there something inside the ECU that can be fried by shorting who knows what he did out ?
He easily toasted the ECU.
The good news is that it may have simply damaged the easily fixed regulator inside the ECU. The bad news is that it may be hard to find someone to replace it.
I would offer to help, but I don't have anything here to try it on and test it out.
Speaking of regulators. The regulator/rectifier was easily smoked.
ALSO, check the cables again on the battery. there are multiple cables there, and you may still have a 'hot' wire on the ground post, or something like that.