Fun fact, if you click the "Instances" button in the bottom right of the page on any instance, you can see what other instances it's connected with, and if you scroll down far enough, which ones are blocked/defederated.
For reference, the instance we're on, lemmynsfw, has 4 instances blocked.
From my (admittedly limited) understanding, the servers pull posts when someone requests them rather than them being actively pushed, which happens regardless of federation status since all those posts and comments are publicly accessible. It was part of the whole "defederate meta's Threads" debate.
You can still see them from here. Defederation is one-way. It just means, if you comment/vote on any post from there, the comment won't spread to other instances.
"I'll know 'em when I see em."
So adorable it got this lemmy instance defederated from blahaj.zone.
Announcement from Lemmynsfw: https://lemmynsfw.com/post/418317
Announcement from Blahaj: https://lemmy.blahaj.zone/post/1204784
Tldr, the admin from Blahaj thought this post looked like CP (it's not, she's a verified OnlyFans model), and wanted the community purged. The Lemmynsfw admin disagreed. The Blahaj admin defederated from Lemmynsfw (they don't get our posts over there anymore). The chat logs between the admins are available in the comments of the Lemmynsfw announcement.