Ah, that makes sense.

I still wonder if there's a way to start a lemmy post from hubzilla without explicitly tagging the community, since it kind of seems like a nuisance on Lemmy's side and is exactly the kind of behaviour mastodon users interacting with lemmy get flamed for.

I guess this is the best I can do though 😅

Asked differently,

what is it that allows lemmy/piefed/mbin to post to a community without explicitly tagging it, but doesn't let hubzilla do the same even though it has a (relatively similar) notion of forum channels?

Ah, that's not what I'm saying though (unless I'm misunderstanding you)

It was more along the lines of me wondering why I STILL need to make my post public to post to lemmy. I set the visibility to the forum, and I want to post it there itself. Why isn't lemmy - hubzilla federation working this way?

It's not like, if I restrict a post, it's not visible on my hubzilla hub anymore. Or are you saying that just because of the way lemmy/hubzilla works, it simply cannot do that interop?