Somehow I, on a single-user instance, have a charming federated timeline that includes a number of people I don't follow.
I suppose it makes sense, as I think favs are federated to followers (and then proactively fetched if not private), so I get to see things fav'd by people I follow even if I don't follow the original poster, but it did still take me, uh, many years to realize this would be the result. Neat.
@Lady Hm, this is possible. A quick review of entries on my FTL shows that's plausibly the case for most of the messages, but there are a few I can't quite account for. (No reblog count seen by my instance, and no replies to the message, but earlier messages in the same thread did have replies, for example.)