The racing line at Pocono's Turn One is to drift to the outside on exit. The outside pass on any track is as dangerous as any pass in racing. The question is not why did Rusty drift up, but rather why did Steve try sticking the nose of his car in between the 2 and the wall?
In my opinion, it was very poor judgement on Steve's part. He was afterall in the overtaking car and there was something like 500 miles to go. Races are never won on the first lap, but many are lost.