I thought beehaw defederating from us would not affect post/comments on shared instances which are neither defederated from them nor us:

lemmy.world/post/149743

Why do I see posts/comments from beehaw users on communities outside lemmy.world and beehaw.org?

That’s because the “true” version of those posts is outside beehaw. So we get updates from those posts. And lemmy.world didn’t defederate beehaw, so posts/comments from beehaw users can still come to versions hosted on lemmy.world.