According to the artist's comment, yes. This was intentional. It was written "I finished P4 and when I saw Ameno, it was stuck to my chest and I thought, "It's the 3rd eye!"
Chinchen said: I would have loved it more if it was actually Koishi, instead of Satori. Cause, you know, the one being possessed by Ameno Sagiri was one of the true criminals of the story. Which was the whole ''Extra arc'' thing.
Nah, that'd be Izanami. Also, this really took long enough.