Well. Peter had asked, hadn't he? And frankly, he hadn't really known what he'd been expecting with that anyway. There was no way the story was going to be anything beside batshit crazy.
So. It wasn't even really a shock. Peter just nodded along and decided that sure, why not. That's what happened in weird worlds that had mushroom people in them.
He was best friends with a raccoon. It wasn't that weird.