Is this not similar to the cab drivers hippocampus. I was a cab driver for around 10 years and I was surprised how easily I managed to learn the streets and routes of a medium sized city, and then recall them without conscious effort.
This is not directly comparable with memorising lyrics and music of course but would likely involve the same part of the brain. A musician who has been at it for years will have songs and tunes programmed into his head.
I can see a song title and recall the melody even though I have not heard it or thought about it for years.
Its a very deep subject.
Roger.