Think? Hmm... Did you see the video? It is not even stable at 720p.
I think what he is saying is that in game the game looks smooth...
How to explain? Well... take Monza for example... in GT5 you can see the tearing clear and in GT6 not... the framerate can be worse causing some kind of trembling in low speeds but the tearing found in GT5 gone... so the game seems smooth.
720p you can't see even the trembling... it is perfect.
I think what we need to see here if the variable framerate is better implemented than GT5... there are games that works with variable framerate being smooth.
I'm not saying it is good... I'm saying the drop in framerate cause a lot more tearing in GT5 than GT6.