My Professor thinks class ends 30 minutes earlier than it does
Who said it was 2.5 hrs?  The schedule?  It is not uncommon for professors to reserve a longer time than is always necessary, just to give themselves a bit of lee-way, in case they sometimes need a bit longer.  A 2.5 h time-slot it not necessarily a commitment to hold class for that long (but check your institutional rules if you feel cheated).  The first class of a term is also often shorter.

The above is true at least for the Australian National University.

In any case, if you will ask him, it pays always to be polite and not to come across as though you are accusing him of intentional wrong-doing; but rather as if you are ignorant of their traditions.