You do "follow" that instance because you are part of kbin.social which is federated with it. You could go in and block each of the magazines/threads from there or whatever the term is on Lemmy, and block the users you don't want to see content from, but kbin.social is federated with lemmynsfw, so that content has the ability to show up in your "all" or "random" feeds unless we defederate -which is the question being asked. So you very well could really l easily have that content in your feed in the best future