That's an interesting point. I wonder if the Messanger button in the Facebook app would fall under this restriction: App Store Review Guidelines 2.14 Apps that are intended to provide trick or fake functionality that are not clearly marked as such will be rejected.
Does the Messenger button within the Facebook app that clearly looks like other buttons that function only within the app "trick" users?
Yeah, not sure how they are getting away with leaving that in there. If they insist on everyone using Messanger they really need to axe the button.