It looked/sounded to me like Stewart was trying to avoid the guy when you hear the engine revving and can see his car swerve.
Agree the guy's a dumbass for walking accross a track during a race.
According to other drivers, a sprint car will have the back end slightly fishtail, or "swerve," when you hit the throttle and rev the engine. Also according to other drivers, Tony Stewart was revving his engine as a means of responding to Kevin Ward's gestures. There's no other reason to suddenly and briefly rev your engine while under caution.
Stewart, having grown up driving these sprint cars, was at least reckless because he knew how the car would react and shouldn't have attempted such a maneuver while going by a driver. Of course, Ward contributed to this by being on the track in the first place, but Stewart certainly didn't help the situation by making his car fish tail while driving by him.
Only Stewart knows, but I don't think it was intentional. Nonetheless, he's well known for being a hothead and probably made a reckless decision that he shouldn't have made.