I think 'Guest' may have it wrong. Most 'Catters are musicians, some are performing, some are appreciating.
Not withstanding my earlier comments, I Do consider myself a 'musician' although my main instrument is 'voice', I have a fairly catholic knowledge of songs and of music.
I feel this is the opposite of the classic 'Marx' quote: "I wouldn't wish to belong to any club which would have me as a member'." The wish to be a 'Catter shows sufficient interest in the genre to identify someone as a musician. Even if the person "Couldn't carry a tune in a bucket" This is only my personal opinion!!!