My first instinct was it might be a function on the server that calculcates the years passed dynamically from today. A quick look with Wayback Machine showed this number 22 is hardcored into the webpage. So the question is, what that means. Obviously it cannot be 22 years ago from the time of writing the article. Valve didn't exist in 1987. Quake came out in 1996 and then someone did the Team Fortress mod for that game. Which Valve created the standalone game Team Fortress Classic a few years later. And Team Fortress 2 came out 2007 (it wasn't Free to Play back then).
Or do he refer to some ideas written on paper, but was not able to create a game with it back in the 80s? Or it's just a typo and I over analyze this. I need help. Medic!
Given that in the very same post he wrote "we need to go back, way back, into the mists of time, when dinosaurs roamed the earth, and we started working on TF2", did you consider it could just be a joke?
I didn't consider this to be intentional. But given that part and context (Valve loves to make jokes), this could be it. Either it is a typo or an intentional joke, which is also likely.
My guess is a typo, possibly supposed to be 11 or 12? Is 1998 too early for TF2 design to be occurring?
Team Fortress 2 was announced in 1998
According to Wikipedia. So that looks plausible.
The post however talks about gathering feedback from players of TFC, which didn't come out until 99. Maybe Robin meant the original mod, which he also worked on, or maybe he just misremembered at what point TFC came out or when they actually explored the death stuff that resulted in the freezecam.