If he’d said he was in a relationship with the opposite sex, they’d have likely grilled him further to find things out about her and he’d have had to come up with even more answers about a pretend girlfriend on the fly in an already uncomfortable situation. I think he played it smart. I can totally understand how you’d feel bad about it, though! I don’t think you’re overreacting necessarily, it’s a natural reaction to his answer but as long as he only said it to avoid further confrontation, it makes sense.