Looked to me like Stewart swerved but not to hit him but to try to dodge him and the guy was just in the way. It’s hard to control something going that fast.
It was a very tragic, unfortunate accident. It WAS crazy to walk out on a track filled with fast-moving machines, though!
FYI the car was going only about 45 mph at that point. It would be more accurate to say a sprint car going that slow on dirt is cumbersome to steer.