Interesting story but according to the posting below, both Robbie Bachman, media sources and Norman Durkee himself have stated that he was actually at the studio as a musician, recording ads in the next room, when summoned by sound engineer Buzz Richmond. According to this version of events, Durkee had only a few minutes to spare, and, quickly conferring with Randy Bachman, he scribbled down the chords (on a pizza box), and, without listening to the song beforehand, recorded the piano part in one take.
en.wikipedia.org