Both colleges use merit aid to help shape the class they want.
Temple is using it because your son is likely at the top end of their applicants, stats wise. Pitt is using it because your son is an attractive applicant who they’d love to have- but likely “above average” in terms of the rest of the applicant pool-- so if he says no, there are more like him to come.
Both colleges would be delighted with a quick yes however- so that’s your son’s leverage with Pitt.