It's just ripping the data straight from Steam which in turn doesn't do the bestest job of tracking that data. I know for a fact I've played a lot more Team Fortress 2 than it lists, but it was before the medic update even. It's not strictly speaking accurate, and being offline playing a single player game probably alters my stuff a bit as well.
Comments
Also:
http://www.lambentstew.com/webblog/miniproject/steamanalysis?steamid=awfurious
Full Steam Analysis Profile: http://lambentstew.com/webblog/miniproject/steamanalysis?steamid=creamsteak
Full Steam Analysis Profile: http://lambentstew.com/webblog/miniproject/steamanalysis?profileid=76561197966641273
http://www.lambentstew.com/webblog/miniproject/steamanalysis
God have mercy on my soul.
http://www.lambentstew.com/webblog/miniproject/steamanalysis
It's mostly that probably 10 or so of the games on the unplayed list are expansions/DLC, and that I know I've played many of them before.