Another point might be that this person can't bake or doesn't like Pumpkin pie. (I have to admit I am not a fan). It might also help at future "potluck" style events to ask people to bring something from a category of foods (dessert, side, salad, etc.) rather than a specific Item. While it doesn't excuse this person, it may have made things easier. Being asked to bring something They can't or won't be eating does alter things a little. (not an excuse, but it may have made the invitation awkward for them)
And it is customary not to invite a guest that doesn't RSVP properly to the next event (or 2), but IF you might like this person, I wouldn't "ban" them outright for the first mistake or mis-step. Just be sure to be very clear about expectations with all your guests (especially newcomers) in future.