Actually, now that I read through the thread from 2004, it appears maybe it was the IP and then my ISP probably provided a name and phone number. The Sect Service guy then called me, and I may have given him my employer information in that first call. I don’t remember every detail anymore. It was just a weird situation.
Once they have your name, I expect it's not so hard for them to find out where you work. Especially if they ask, and you answer.
If you had posted from work, their task would have been tougher. Only the more organized employers would be tracking which computer accessed which web site through the company connection.
Posting from a WiFi hotspot would be even tougher. They might get lucky interviewing the hotspot provider: Oh, yeah, there's this one guy who hangs out a table in the back sipping his latte. Doaks, I believe. Joe Doaks. Always uses his Visa card ...
On the other hand, if you post from work, from home, and from random hotspots, then it gets easy ...