You’re confusing something. Defederation by lemmy.ml means that lemmy.ml users cannot see any threads.net content if they wanted or not. Threads.net can still connect to lemmy.ml. That’s exactly the situation lemmy.world and beehaw.org are in: beehaw.org blocked lemmy.world and lemmy.world users can see and interact with everything from beehaw.org, just beehaw users don’t see any of those interactions. Have a look at lemmy.world/c/[email protected] as proof.