I absolutely believe Ward did a dumb thing for getting out of his car and trying to do whatever it is he was trying to do on the track. However, I don't know if I believe Stewart just didn't see him. Maybe he thought he'd swerve by him and clip his foot or hand or something, or even just swerve close and scare him good. But when there is a car stopped, you should always, always try to move as far away as possible when passing it. They were already under a caution flag due to the vehicle being disabled. If you watch the video, you can see that other drivers are slowing down and moving away. It doesn't look like Stewart did.
Do I think he intended to full on hit him and kill him? No way. Not at all. Do I think it was a road rage type of thing? Maybe. Obviously Ward was upset at Stewart, who knows what frame of mind Stewart was in. Maybe he meant to just scare him and it turned out awful. Maybe he truly didn't see him. But I don't understand how it would have happened, even if he just didn't see him. He should have been driving extremely cautiously, especially near the stopped car.