I still think it could have been your friend. How do you KNOW he wasn't online? Its rather easy to have more than one name, and you said yourself that only HE knew about that name. So I assume you have more then one, and this one is your anonymous name... wouldn't it sound logical if your friend had one of those names too? Perhaps the one you ran into is your friend's anonymous name as well.
Aside from that, did he say "Hi" everytime someone entered?
He coulda been randomly luck, Psychic, WhackJob, or just your friend. My bet is the first or the last (although your friend might also be a whackjob
).
As for the name 'warlock'........ I've played video games with someone using the name of GOD, it never made me wonder.. "Did I just frag God?" Its just a name, maybe he's a fantasy role-player, or gothy, or had a name that he could use to fit into chats. Think nothing of the name, until they prove to you otherwise. I really doubt you look at my name, and wonder if my face is constantly covered with Nickoledean Gak, (not how the name was derived mind you) but that is the name. Thus my point.