i can see comments from explosive heads users, which unfortunatly, my instance (lemmy grad) is still federated with them

https://lemmygrad.ml/instances

https://fba.ryona.agency/?reverse=lemmygrad.ml

Both see exploding-heads.com blocked by lemmygrad.ml, apparently since 2023-06-15. Are the comments you see older than this? You shouldn't see any e-h activity on lg communities after that date. Or you're viewing the local copy of a lemmygrad community on exploding-heads, but in this case you should only see e-h comments after that date.