If the Prius is a ‘fly by wire’ type of vehicle, then I would think if one turned it off and then back on the glitch would clear and the driver would have control again.
I believe what you wrote is correct, but it would require someone to hold a button for X seconds, similar to holding the power key on your computer for 5” to shut it off.
If someone is in a car that is accelerating and they can’t get the car into neutral, they might panic and never think about it. I’ve met lots of folks that didn’t know you can stop your laptop by holding the power key down until it dies - and laptops aren’t going 80 mph!