The difference between a musician and a non-musician listening to music is that the musician has a strong tendency to get absorbed in the technical musical aspects of the performance, such as whether the right notes are being hit at the right time with the right inflection. When they listen they are prone to "play along" with the music in their mind with their own imaginary instrument. They might even move their fingers a bit or not.
Most non-musicians lack the musical technical knowledge that it takes to listen to music like a musician. They listen more holistically and are generally far more concerned with how the music is acted on by the sound system or the room. The details are more interesting to the musician.
This strikes a deep chord with me (ok, no pun intended). When I listen to most music I am definitely, in my head, playing lead guitar, then the next moment I'm playing the bass, then I'm playing the drums, then I'm playing the guitar again, etc. LOL, I'm never picturing myself as the singer I see and feel the frets on the guitar neck, I feel my thumb, index and middle fingers plucking the strings on the bass. I see the progressions. I absolutely go nuts when I hear unusual syncopations. Give me Floyd's Money in 7/4 or Genesis's Robbery, Assault And Battery in 13/8. Don't give me no boring 4/4 music.