Correction - The video is from a Germany team. And they graciously share the following programming / design trick with others:
Halljac (1 week ago)
how do you get the robot to follow the black line so smoothly?
robodream (1 week ago)
We follow the line with one light sensor on the "inside" of the bend. Outside motor running all the time, inside motor full powerlevel when seeing white, backwards 20% powerlevel when seeing black. We get the speed by putting the big gearwheel on the NXT Servomotor and the medium gearwheel on the chain shaft.