Purely not true. First of all, there was ~ at that time ~ no rule against drivers getting out of wrecked or immobile cars. Secondly, even though he was on the track (which a LOT of drivers have done, including Tony Stewart himself), it does not make him fair game for getting hit or run over.
Stewart may not have deliberately hit Ward, but there are other considerations such as recklessness, carelessness, negligence, endangerment, etc., against which Stewart's conduct will be evaluated against.
I don't think Stewart deliberately injured or killed Ward, but if he wanted to 'buzz' Ward to show him who was who, he may have shown such indifference to the potential consequences for his actions that it may rise to the level of a misdemeanor crime. I don't know, and I'm glad I'm not on that grand jury.