This happened with the sniper update (not sure if it was talked about in this thread, can't remember), every now and then they changed the image for about a minute of the sniper standing over a dead spy, to a sniper standing of a (feigned) dead spy with a cloaked spy behind him, this was the clue that it would be a double update. So either valve are having a bit of a laugh, or Jarate really is the 3rd unlock!
Also, Jarate is one of the presets on the computer screen in Meet the Spy.