And of course your response should have been "I'll cut the feed to it, your guys can clean it up"
Everybody wants someone else to do the work. Did he offer to pay more for the clean-up?
BTW, that is horrible. No telling what all is in that mess.
That is essentially whats happening.
I'm not sure what kind of battery acid they used to clean stuff with... But rotted through the disposal, flowed inside the flex into the box and down the wall. Eating everything in its path. This section of wall is coming out.
I was actually really surprised it had not shorted yet, and still worked! A lot of the insulation was eaten off.
(Before anyone gets worried... it's a wye system, and the ground and neutral are good.)