Hasn't been in Mystic Falls for a long, long time? That doesn't make sense to her. After the veil went back up, Anna hung around, watching and waiting, observing and commenting to the literal dead air around her that was incapable of responding or transferring her words to the living realm. Damon was there. She saw him. If it had been someone wearing a Damon mask, she would've known. She saw so much from the Other Side that people didn't usually see; she would've saw that, would've sensed it.

"You do when someone pulls down the veil between the real world and the Other Side. You can't tell me you don't remember that."