I'm pretty sure that means that if a Beehaw user is blocked from Lemmy.world, they can still comment on posts federated from Lemmy.world to Beehaw. In the Beehaw duplicate community. But when content from the specific user is sent back to Lemmy.world, the instance refuse to accept the comment either due to the individual being banned from the controlling community on Lemmy.world or from the instance as a whole.
At least that's how it seemed to work in late 2022 when I administered my own instance and people were intensely ban and block happy on the instance level.
But isn't it easy to test? I'll make a community on my home instance and you subscribe to it so it's federated to Lemmy.world and then you simply remove the content from Lemmy.world, yes?
What can I say? If people can't accept that other people might have different opinions and worldview, it's not people I think I'd miss the opportunity to interact with. So I don't really lament those who block my home instance.
To address your surprise; it seems that the majority of new people coming to the Lemmyverse are reasonable and thinking people.