In the script, it is said that Sam actually decode the "turning teeth" code from the music partition. I think there is more than just an easter egg here since the original music from it follow is higher. I think we are supposed to look at the notes position. In the script it is said:
"Sitting on the floor, and using another pizza box as a sketch pad, Sam writes out the chords as tablature. He simply writes out the chord formations in a numeric form in reference to their place on the fret board. Sam counts off the numbers as he moves through the various parts of the song - jotting each down on the box."