The cars inside are going as fast as they can, with only the grip of their tires keeping them in the race line. The car along the wall can go much faster, as fast as it engine can push it because the wall keeps the car in the track. The grip of the tires is not the limit anymore.
Unfortunately the wall also destroys the car so this is a trick that can't be done more than once per race. If they don't agree not to do it again everybody will have to race like that on the last lap of those short tracks, to defend from the drivers behind. The costs for the car and maybe for the track (restoring the walls?) will be substantial. Check the pictures of the right side of the #1 car.
Unfortunately the wall also destroys the car so this is a trick that can't be done more than once per race. If they don't agree not to do it again everybody will have to race like that on the last lap of those short tracks, to defend from the drivers behind. The costs for the car and maybe for the track (restoring the walls?) will be substantial. Check the pictures of the right side of the #1 car.