Very interesting. I believe, if I may offer my impression, that the great performer is referring to gravitation, but not to the exclusive manner in which to perform the Impressionists. What she cites is the indispensable confidence that the pianist must gain from themselves regarding the "contact" with the keyboard. This is one of the essential principles for developing good technique in general, but, I believe, fundamental in the Impressionists. The relaxation of the arm and shoulder leads to an awareness of the bottom of the key and the contact with it. I remember achieving a good result in a concert during the final part of the first of the "Estampes". With extreme adherence and gravitation, controlled by the shoulder, I managed to obtain good "nuances" even at pianissimo. I will post these recordings of mine in the Audio section. Naturally, the piano was prepared with the first escapement very close to the strings, decreasing both the hammer let-off and, above all, decreasing the strength of the repetition lever spring. This was requested by me because the instrument, although quite new, was not very large and the keyboard was therefore not so docile due to the "short lever" of the key. Naturally, in this type of technique, shoulder control is fundamental, just as the rotation gesture also assumes great importance.