Rachmaninoff Prelude in c# minor

In one scene, Stet walks into an empty auditorium as Dustin Hoffman is playing this piece on the grand piano onstage. Does anyone know whether he is really playing it? It certainly looks so-- if not, it is a daring and convincing pantomime, and a commendable detail either way. More often, when actors are supposed to be playing the piano, we don't even see their hands. Another exception comes to mind: Dudley Moore in "Arthur." He was an accomplished pianist in real life (as well as a connoisseur of English cathedral choirs, who would have loved the theme of this film, probably enough to aspire to Hoffman's part were he still alive).

Didn't I read somewhere that Hoffman actually studied the piano in his youth but wasn't talented enough to make a career of it? If so, then this scene was a poignant autobiographical glimpse.