Ward also didn't put himself as close to them as he did Stewart's car. He singled him out and was looking for him evidenced by the hand gestures. It makes perfect sense that Stewart gunned it to the left to try and avoid hitting him when he saw the dummy was too close. On that kind of rear end (posi) with a banked track, if he gives it gas to the LEFT, the right tire ONLY would have had traction thus fish tailing the car back to the right afterwards.
To me, its just a sad and unfortunate accident. Tony meant no harm to this guy. And again, going back to the root cause, this guy's own negligence and stupidity caused it. Not Stewart.
It's hard to tell whether Ward put himself closer to Stewart. Yeah, he was looking for him so as to point at him, and was moving down the track until at least right before the #45 car came by, but the fact that Stewart came so close is in part due to the fact that he was higher up on the track. You can tell that Stewart is riding higher on the track than several of the other cars, including the #45 directly in front of him. However, I don't know whether he was that high before he came into the frame, or whether he was lower on the track and then went higher in an attempt to "buzz" Ward. The limited view and jittery camera work doesn't help to determine a lot of things.
But my main point is that
if Stewart revved the engine in an attempt to swing the car so as to scare Ward, that's reckless. And while Ward put himself in that situation, it's not fair to take all blame off of Stewart for doing something dumb if he was aware of Ward being on the track and was trying to scare him. Again, I don't
know that's what happened, but like jmar said, it's certainly not unlike Stewart and isn't outside the realm of possibilities.
It's sort of like saying that a kid was stupid for playing in the street, and that a driver who hits the kid because they wanted to get as close as possible to scare them from ever wanting to play in the street again is not in the wrong or culpable to any degree for the resulting death of the kid. Person A's initial stupidity/recklessness does not give Person B free reign to do whatever and not be held liable. You still have the responsibility to act reasonably and avoid causing harm. Whether you're able to reasonably do so is certainly a defense, but that defense usually goes out the window if you also act recklessly. At that point in time, comparative or contributory negligence (depending on the state) would determine Stewart's civil liability, and it would also play a part if any criminal charges were brought.