In the video, the car has no problem going into neutral at 80mph, even if the pedal is pinned to the floor. The car also has no problem slowing down if the brakes are depressed, again while driving 80mph ("myl'n ahwer") with the throttle pinned.
And on Youtube, this video also shows what happens when you press the brake and gas a the same time on a Prius while moving. Again, no problem slowing down.
In both videos, you can clearly hear the engine noise cut out when the brakes are pressed. That's because the 2008 Prius already has a sort of brake override software, in the sense that the hybrid powertrain controls system doesn't see a need to waste gas if the driver is trying to brake. So if you hit the brakes and the throttle at the same time, the hybrid will reduce engine torque.
So what happened with Sikes in California? How did his Prius keep going, while he was supposedly standing on the brake pedal?