If you compare your link, on Lemmy world to beehaw.org/post/931057 the same post viewed through beehaw directly, you will see completely different comments. And the Lenny.world link only has comments from Lemmy.world users.
Defederation behaves in a very confusing way. It blocks interacting with a community, but not the content itself. You can see beehaw’s posts, they can see Lemmy.world’s posts. Comments are not shared, and any posts to unfederated instances never leave the instances they were written on.