How did he "track it back to the chat room"? What evidence is there it was anything at all to do with this site?
There is no virus on the chat room, but if you clicked links other people posted you could have gone to some dodgy sites that may have viruses.
I've never seen anyone post a bad site on the chat though so it was very likely another site you visited or something you downloaded. Also make sure you have the firewall turned on (Windows should tell you if it isn't) as there is a small possibility someone could gain unauthorized access to your PC. And make sure your computer is getting updated regularly (Windows Update).