The teacher dealing with tests would absolutely have had that same stance for a visiting relative or for a Dr. appt, both of which are somewhat a matter of choice in relation to timing.  You can choose when to schedule a Dr. appt, or a family visit, a religious holiday is fixed on the calendar, I can't exactly reschedule Rosh Hashanah.  Hell, many calendars even list the Jewish holidays, so it isn't like this is some kind of a secret.  As for a Christian holiday, based on his other behavior, as long as it was what he would consider a mainstream sect of Christianity, he probably wouldn't have had any problem, but if you were a Mormon or Jehova's Witness, he most probably would have.  I don't know if either have holidays that are different than the mainstream Christian ones.

This is the same school system that threatened to fail a Jehova's Witness girl who didn't want to go to the big Christmas display as part of a school trip.  As far as I remember, it isn't allowed in her religion.