I don't buy it. Heck, I've even stepped on the gas instead of the brake. Besides, the brakes are much more effective than that little Toyota engine is. Try it yourself. Go full throttle and step hard on the brake. You'll stop.
With wide open throttle, why would the power brakes lose vacuum? Vacuum is lost when the engine quits.
Besides, just to stand on one foot requires 100 lbs of force exerted on your foot. If you can walk, you can do that. Pressing with 175 lbs is not a problem.
The point is, the brakes can override the engine torque. Unless, of course, you're standing on the gas instead of the brake.
You can also just turn the key off on a runaway engine.
