Actually this points to his story being incorrect. If he slammed on the brakes and the car continued to accelerate than he probably slammed on the gas by accident instead. Testing shows that if you slam on the brakes while the engine is pegged at full throttle, you'll still come to a screeching halt. The brake system vastly overpowers the engine even in high powered cars. In a Camry V6 it actually takes just 16 feet further to stop from 70mph with the throttle wide open at 190ft vs. 174ft.
And the brake system is not drive-by-wire like the throttle is, so it's not susceptible to faulty ECU problems.