Hmm, I don't know. I don't think there is a favorites. Maybe it's showing up on their recently viewed list? Like, they recently viewed you and then it shows you're online?
When I was on OKCupid - there was a favorites option. I think it would notify you though when someone favorited you. What always creeped me out was when I'd get a notification I'd been favorited and they had never contacted me.