I have to disagree malmo. I don't expect you to give one inch just like smoke, but two things suggest to me that the revved engine heard in the video is Stewart's:
1. The ~20 seconds before the loud rev, you don't hear ANY sounds of that magnitude, as the other cars are idling under caution at that point.
2. Apart from a very slight delay due to distance, the sound perfectly matches the timing of the aggressive sliding maneuver of Stewart's car. It seems to be generally accepted that hitting the gas causes these cars to slide, and the sound lasts just as long as the car is sliding.
Basically, it would have to be a pretty well timed coincidence for the first loud rev in over 20 seconds to come from a nearby car at the same exact time that Stewart is aggressively maneuvering. Occam's Razor says the sound came from Stewart's car.
As for the sound of the crash not being heard:
1. The other cars were still racing full tilt when that happened, thus they would drown out the sound much more so than when they were idling under caution.
2. A full throttle engine is much louder than a crash, or at least a crash at that moderate speed.