Not that this makes it okay but there's a chance the person just didn't know and made an honest mistake. In general, especially during finals week, restaurant employees are part time. It's not out of the realm of possibility that whoever answered the phone had no idea they were taking reservations when they never do. Hell, sometimes I take a week off of work and return to a whole new set of rules
Either way, I hope you let the incident roll off your back and enjoyed your meal. I make a note never to dine with someone again when they let a restaurant mishap ruin good company.