Unrestricted paid ticket is still available to students

Open Events → Events → select your event → Edit Event → Ticketing.

A free Student-restricted ticket does not make an unrestricted paid ticket non-student-only. The unrestricted type remains eligible for students as well. Registrant restrictions inspect the registrant's affiliations; guest restrictions inspect the attendee's. Configure the appropriate audiences and collect affiliations, then test student/nonstudent cases. Do not assume that missing affiliation data reveals all restricted ticket types.