Not on a car with electronic throttle control. That would be any car 2005 or newer. The PCM (powertrain control Module) has full control of the accelerator. ABS, skid control and traction control have brake control. If all ABS solenoids were in pressure reduction mode (hacked) there would be no brakes. Electric power steering on many new cars too. All computer controlled.
I know what you are stating. That is all true.
BUT.... there is a spring on the accelerator pedal. Otherwise, it would never return to full up position. All the electronics in the world doesn't change the design of the accelerator pedal itself.
Now... I doubt that this is the way they rigged it (assuming they did) because it would involve access to the inside and underhood of the car. Possbile, but not likely.
It is more likely that they just accessed the car computer via a wireless link. If your vehicle has Cruise Control, it can push the pedal FOR YOU. If it gets a signal the FLOOR IT, that's what it does.
If you mash the brakes and the gas, the gas wins.