Magic. Jon only knew of one person with magic, Stannis' Red Woman, and he hadn't trusted it at all. There was some magic spoken of as far as Daenerys Targaryen was concerned but as he hadn't met the woman, he couldn't speak to it. He could only speak to what he knew and none of it was good. Still. This woman didn't seem like the priestess.

"Magic. Do you use the blood of innocents to work this magic? That is how it works in Westeros."