Looking at that video, I don't think Stewart was driving "that" fast. He appeared to be driving the same speed (caution) as the other drivers.
The driver who wiped out is more to blame than Stewart.
He appeared to be wanting to confront the driver that sent him into the wall by standing in the middle of the track. Granted it was Stewart who put that driver into the wall, but even that didn't look to be on purpose. Although, it is Sprint car, so that very well could have been intentional.
It was night and that driver was dressed in black, which would make him even more difficult to see.
When Stewart initially hit the driver, his vehicle swerves, which looks as if that swerve is caused by the impact.
IMO I don't think Stewart maliciously went after that guy. Just an unfortunate set of circumstances.
Let's see what the investigation shows .....