Right, that was Keir Dullea in one of the school's practice rooms, IIRC. I can't look at the clip easily, but that must be it. Fantastic movie.
I could have sworn I figured out whose composition (or maybe improvisation) it was a long time ago, but it's definitely not Messiaen. And I definitely don't remember whatever conclusion I came to.
Anyway, I don't really "have" Twitter either, except for some account I no longer remember the login details for.
But that's interesting enough to make me want to ask Zittrer myself.
Might get more of an "official" response if someone with the power to do like a group post from "Pianostreet.com" I highly doubt the producers know or recall that kind of detail. I don't remember the director's name, but if he or she is still around, could even be a better or equal source of information. The editor might remember as well, or the sound designer.