I didn't even think of calling the other contractor. That's the best way to handle it. If it was my guy screwing up like that I'd want to know too. That's the what to do...
The what to say to the homeowner..... You don't have to make up excuses and try to justify what the other guy did or that it was an "honest mistake". If their tech truly didn't know what he was doing (which sounds like the case to me) then either the boss is dishonestly sending out a guy to a call calling him an electrician, or the tech is dishonestly selling himself to the boss as qualified. I'd avoid bashing the guy, but that doesn't leave the other option as talk him up. When in doubt, less said is often better.
