In piano performance you often can hear the mechanical sound of the keys themselves as well as the breathing and humming noises from the pianist. Not to mention a performance will be played in an environment where environmental sounds will be correlated with the perception of timber and the pianists physical movements. I don’t see mention if they controlled for all these things.
eg: the Keith Jarrett / David Helfgott recording inversion, performances where you can often hear the notes of the piano over the sounds of the pianist.
