I don't think anyone cares any more about 4chan stuff, but uhh...
He joined the channel like anyone else would have, just like the cygnus guy. We knew who they were (although not initially for cygnus, he wasn't a #4chan mod yet), but decided to treat them as regular people and see what would happen. Maybe they'd stop treating us as adversaries?
But, it turns out that just like janitors and mods in the past, their reason for entering the channel was use it as a monitoring system to enhance their moderation. As a result every known irc handle of 4chan staff is banned from #qa. The real mystery is why they used their actual handles, especially since the presumption was they were still there with different ones since there's always been 5-10 people in the channel that never talk.