I definitely remember it being explained to me but god that was months ago. Maybe I am just conflating various aspects. I'll see if I can find it, maybe it was just speculation mixed with information; this is the problem with playing this leaker telephoneKhu has said it "explains the face on the base of Terra ornaments" (in response to Kaka saying that it might be in DLC) and that "you would see 3 more brand new pokemon in game", also saying the model isn't there. I haven't heard of him saying anything more specific than that and Kaka has been gone since September so he couldn't have commented on the ingame stuff mentioned in October.
Speaking of which, recently Khu did mention that you have to find "3" when referring to today's book reveal as well.
EDIT:
You may be thinking of the poll where the 3rd legendary was an option among the professors, Arven, and the box legendaries, but the answer was never specified.