Instance blocking is based on author, not community

Blocking an instance is determined by the submitting author, not the community the article is submitted to. So if I see a post in the fake community memes@whitepower.ml and want to block white power.ml, but the post was submitted by bob@normalemmy.me, I will block normalemmy.me instead of whitepower.ml.

Is that expected behavior? Because it was not to me.