Dude, what part of preseason don't you understand? Please, stop trying to pin what type of back he's going to be by 6 runs in his first preseason game. And string? You're saying he went vs. 2nd string? I'm sure he had players on his team too, blocking, etc who weren't first team. Or maybe they're trying new things, guys are rusty etc.
Other players who didn't do well don't try in preseason though? :
Joe Addai, 4/0 WITH his long run.
F.Jones had 5/13 if you take out his long run.
Larry Johnson 7/11 without his long run.
Reggie Bush 6/11 without his long run.
K.Smith, 7/15 without his long run.
R.Rice, 5/7 without long run.
Maroney, 5/0 wihtout long run.
Selvin Young, 3/-4 without his long run.
M.Lynch, 2/4 without his long run.
J.Lewis, 2/0 without his long run.
Thomas Jones, 3/6 without his long run.
Frank Gore, 1/0 without his long run.
See how ridiculous this game of yours is?
For further information, please watch this for more ridiculousness, and proof he doesn't just try to "outrun" others: