That's the possibility I'm wondering about. I wasn't really imagining they would pretend it was posted by someone you're following but surround it with some Sponsored content message that made it clear they injected it into the feed of the person you are following.

It sure seems like a terrible idea to me, I'm just trying imagine how exactly they could make it go from an interesting idea of federating, to something that is terrible as meta is one to do.

I think probably the real reason they are federating is to avoid anti-trust issues.