Most Helpful Girl
I would just call or text him to clear up the misunderstanding. He's got to be joking if he thinks asking someone to join you for lunch = a date/interested in him.
He needs a reality check but a gentle one. Just tell him that it was all about lunch and hanging out and nothing else and that you look forward to seeing him again at class. When he returns to class, just get on with him like nothing happened and leave it there.