is this real? someone got info or something?

Eddie Kramer discusses this in the Electric Ladyland documentary from several years back (1996?). Part of this clip is played, and Eddie Kramer says something to the effect of "We have a visitor! None other than Brian Jones," and notes that after a few tries, the piano idea was nixed, and that he was given some percussion to play. Mitch Mitchell comments on this in the film as well. The documentary is worth seeking out if you haven't seen it. There are some great interviews with people who worked on the album, plus some amazing Super 8 home movie footage from Noel Redding's collection.