OK I'm going to spoiler this so don't read it if you've not seen the show yet. It'll ruin a good bit for zero reward.
So, the girl was a jazz/folk musician, two seemingly irreconcilable styles of music due to their respective properties, which Lee described. Jazz as freewheeling, unpredictable, searching, innovative. Folk as ancient, traditional, passed down, with no room for improvisation or metamorphosis. Can you spot the inference I immediately made from the punchline (which was delivered looking down, away from the audience, without a smirk or chuckle)?