A lot of 'Unintended Acceleration' has been analysed and concluded to be 'Pedal confusion'. Here's how it works. The driver goes into panic mode (for whatever reason) and wants to stop the car. The driver jams down as hard as possible, with all their might, on what they think is the brake pedal. The feedback from their leg, is that it is pushing on an immovable object (just like a full-on push to the brake pedal), except what they are pushing on is the floorboard, and unfortunately the accelerator pedal is between their foot and the floorboard.
Even racing engines have had the shit comprehensively zinged out of them, by the driver in 'panic mode' (usually after they have gone over the 'edge' in some manner, and there's 'no coming back').