Well, my understanding is that email is federated, and SMS text messages are federated, but it isn't easy to email a phone number, or send a text to someone's email. So I'm surprised that Kbin and Lemmy can talk to each other.
But I see someone else answered that Lemmy, Kbin, and Mastodon all speak the same underlying protocol, ActivityPub. Now it's starting to make sense.
I came here to request /r/BestOfRedditorUpdates, but saw this post indicating there were problems.
Hopefully you can get the name thing sorted out and add this to your copied content.
I think /r/BestOfRedditorUpdates actually would be good for this kind of crossposting, because most of the content is copied into the posts. You don't have to go to the links.