I think it was both people could see fairies and fairies escaped into the world, because at the end, people were talking about how they could see them now.

*runs to find her copy*

Ok, as near as I can tell, everyone saw the big averted merge, and at least some are able to see fairies, because there are two girls talking about it and one is all "nope, mass hallucination" and then they both see one.