Well I can't seem to find his comment. Look at his profile page and it's not showing up, I tried to reopen this thread and it shows 32 comments. But mine and yours are the only one showing up.
No there's something different than that going on. This replies in my inbox, but when I go back to the thread it's not there. I can't see any comments except for the one I replied to, and my own.
Those aren't band accounts making comments. Unless you're trying to tell me my account is banned? I don't know why my account would be banned here.
Well, I'm not really sure about the comment numbers, etc. I saw a pull request solving negative comments in communities, though. So I guess it's still being worked on.
You can tag other users with @username@instance.tld when using the official web UI. I don't know about 3rd party clients, though.