this video is wrong, the throttle can be applied and then taken off (but not fully)
there is a thing called 'beyond smoothness' which means pushing the car beyond the limit and coming back, ayrton senna did it using the throttle, and schumi does it using the steering wheel.
being smooth is a kind of 'cheat' to becoming pretty fast with no feel for what the car is doing, the last few tenths or hundreths are down to feel and 'beyond smoothness'
its very hard to understand! but true.