It sounds about right, my brakes are squeaky (which is common) but they've been squeakin for a while now, almost as long as when the brake job was done.

I hope this is part of the problem with the ABS, even though they can squeak at anytime. Will the backing plates be a reason for the squeaking?

I think he might of touched something and didn't put it back right, especially with the ABS sensors they can be sensitive.