It isn’t complete defederation. In the example I linked from lemmy.world, kbin users can still see and comment on lemmy.world posts. But lemmy.world has made some kbin communities unavailable to lemmy.world users. The issue is a bug in kbin: when a kbin mod removes a post, that removal action isn’t federated to Lemmy instances so the post remains visible to Lemmy users. That loophole is ripe for abuse.
It isn’t complete defederation. In the example I linked from lemmy.world, kbin users can still see and comment on lemmy.world posts. But lemmy.world has made some kbin communities unavailable to lemmy.world users. The issue is a bug in kbin: when a kbin mod removes a post, that removal action isn’t federated to Lemmy instances so the post remains visible to Lemmy users. That loophole is ripe for abuse.