That's referring to the Raw Score only. The adjusted score is based on a huge number of factors such as the raw score, your kill to loss ratio, how long you played, if you used cheats, what the relative handicap differential was between you and the AI, if you won or lost, all that sort of thing. That means that the non-raw score will fluctuate up and down as you play, rather than just counting upwards (as the raw score does).