It's up to TSA to grant or deny PreCheck. If they have approved it, this is normally printed on your boarding pass. No one at the airport is involved with this decision: they should not comment and they should deny you use of the PreCheck line when your boarding pass says PreCheck. However, AFAIK PreCheck currently is given only to USA citizens, (some?) permanent residents, citizens of some other countries, Privium members, etc.; I don't think citizens of certain countries are eligible unless they qualify on one of the other criteria.