I don't know anything about grinding, but that's pretty awesome.
TF2 has achievements, and TF2 has unlockable items like hats and weapons. These used to be tied to the achievements (maybe still are), so you'd need to get 50% of the Pyro achievements to get the new flamethrower, etc. Since some of the achievements are hard to get in regular play and people that don't care about the achievements just wanted the new weapons, maps and servers were set up with special situations to easily "grind" the achievements as quickly as possible to get the weapon unlocks.
EDIT
And yeah, thats hilarious.
