I'm only a man a seller of cheese

The story:

My mom and me were in the car. My older sister had left the song 'superman' playing. We liked the song but couldn't manage to hear anything else at this certain part but " seller of cheese". She convinced my cousin and me that those were the lyrics. My sister got back later that day and told my mom about the lyric mistake, but forget to tell us! We went on thinking that those were the real lyrics! Now whenever we hear that song, we call it the cheese song!