He should have turn the ignition off right away, too bad he didn't
I had a similar experience years ago when I forgot to reattach a spark plug wire holder on my old max wedge car(1963 Plymouth Belvedere sedan) driver side carb and it ended up getting stuck under the throttle linkage making the motor stay at around 3500 RPM in low gear after showing off driving into the yard at work, I went through chain link fence and scratched up some of the trim around the windshield and broke off the "426" emblem off the hood
I got lucky that it didn't do any other damage to the car or me or at work