What does the "community ban" alert actually mean?

This morning I tried to reply to a comment in worldnews@lemmy.world, and got a "community ban" alert.

This seemed odd as I had not been informed that I had been banned from said community by the mods. Doing some testing, I realised I was getting the alert when replying to some users but not others. When using via browser I just got a hanging loading bar when trying to reply to said users.

So, I'm trying to work out what the "community ban" alert actually represts, as I'm not banned from said community, does it represent that users have me blocked, that their instance isn't federated with mine, etc? Any clarification helps.