Until some time ago (a few weeks or so), I’m pretty sure I could still come across comments written by users I blocked. I know that because I started to tag the users because of that. Now I’ve noted that not only comments by blocked users are completely hidden from me, but the entire thread starting from them, including responses by other users, is invisible.
I’m not really sure if that’s the intended behavior (and if it’s piefed or my instance that does it).
I don’t know if Piefed is supposed to handle things differently, but on lemmy, you do neither see posts of users you’ve blocked nor their comments, including their whole reply chain. The only indicator is that the displayed number of replies to a post is larger than the number of replies that are displayed.