If an instance defederates from you, that instance stops seeing stuff from your instance. But not necessarily the other way around, as defederation is a one-way action.
I invite you to check out, say, [email protected] from lemmy.world, and from beehaw.org directly. You'll notice that .world isn't receiving updates from beehaw. A couple of posts seem to have filtered through somehow, but there are almost no posts or comments coming from beehaw.
The group is completely out of sync with its origin. And it's not because .world has blocked beehaw. Beehaw very much still appears under .world's list of linked websites.
Blocked instances are blocked, and when you block communication between sites, that's usually a two-way street.