If a highly rigid piece of the guardrail, such as a bolt) were to catch on a rigid part of the car at those speeds, it could cause a violent reaction that could be difficult for the driver to predict, including sending the car into a spin, bouncing it back onto the road, or puncturing a tire. If the driver reacted incorrectly to any of these situations, he or she might end up colliding with another vehicle, exiting the roadway, or flipping the vehicle over.
Having said that, I'm glad this fellow ended up alright. I'm also quite glad my car has a traditional key and manual transaxle. If my brakes failed or electronic throttle malfunctioned, I do have a few safeguards that can help me out. I'll blow my engine intentionally before I let my vehicle injure me too badly.