He never said anything about the belt looking frayed, shredded, not touching the sides of the pulley or anything else like that.
He said his friend changed the alternator and now the belt squeals.
Don't friken overcomplicate things for no reason until it's necessary guys.
Yes, it even could have been a bad batch of rubber that got missed because it was Friday and everyone had a hangover because the boss had a party at his house and that bad batch of rubber causes problems with the coating on new pully's only from Autozone.
Jees, start with tightening the belt as described in the manual and IF it still squeals, THEN look into the other possibilities.