of course he wanted the first down- thats part of the game. But he clearly saw he wasnt going to get there, and to avoid unneccessary hit, he slid. Which is the exact reason for the rule in place for players giving themselves up.
i could understand that logic if he was upright and running/lunging or reaching for the line to gain. Thats the "want" i think you are referring to here.
However, there is a photo about 5 posts up that clearly shows he starts his slide a full 2 yards FROM the first down?
And im sure you, like Trevor, and everyone else that watches football, understands that a player giving himself up, is DOWN at the moment he initiates the slide.