He doesn't know what to say about it either, though he does lower his head and mumble a quiet "sorry" before falling silent. He knows he shouldn't really be apologizing for existing, and he couldn't have changed everyone's mind about humans, but he still feels strangely guilty.

"Made you remember what...? You shouldn't apologize. I was... you didn't know I would do that. And you... were worried about me."

Or worried about some... other version of him. This Papyrus everyone besides him seems to know.