There are a number of things that could cause a brake squeal. Failure to surface or replace the rotors, failure to clean the rotors after machining or the cleaning of new ones, failure to clean and lube caliper slides, omission of anti-rattle clips, etc.
It’s also unknown if both front and rear were serviced with linings only, if the squealing existed previously, and the possibility that one end was repaired and the noise is from the other.