I'm seeing that a lot as well on my instance. It makes sense in a way. Our instances *could* have done a look up for actors and/or posts and stored that information, for whatever reason.
What bothers me more, is that there are federated platforms out there (Fediverse.blog for instance) that just send out any post to my instance, while I'm not following anyone from that platform at all.
What bothers me more, is that there are federated platforms out there (Fediverse.blog for instance) that just send out any post to my instance, while I'm not following anyone from that platform at all.