The speed in the crash is a relative concept. As some are posting that these cars are "tame" for their purpose, you have to remember that this kid was 24 years old, just turned 24, it was his birthday actually. People posting that they've done this numerous times, in different locations, have these cars, etc, that's great, but there was a time where you were learning to drive it as well. Just because he was going 100 doesn't mean that wasn't beyond him. Perhaps he's never hit 100 in any car before, well, it's gonna feel different. The faster you go, the less time you have to react. The less experience you have at a faster speed, that reaction time is even less. So whether he was going 100 or 150 or 200, if it was his first time doing it and he's not fully aware of what the car is going to do, and it breaks loose, it's over in a flash.
As for the instructor, try as he might to be trying to save the car and prevent the wreck, as I just mentioned, the higher the speed, the less time you have to react and eventually, you're just along for the ride. Even if there's a kill switch, it's not going to stop the forward momentum of the car. Pulling the E break isn't going to stop the car on a dime.
As others have said, you have to respect the car and the speed.
I've seen in some go-kart parks while on vacation, they had one track for the adults, only with real cars, not go karts. They were basically full sized "indy" cars and yes, I saw some people totally "hot shot" it and yeah, they wrecked, bad. Why? They didn't know the car, how it would react or what it was going to do.