Recently while playing in a survival world listening to MInecraft's relaxing music it suddenly started repeating the same note(s)

As in: A B C A A B G G G G G G G G C D*

Or: A B A D G D G D G D G D G D**

*Song repeats note "G"

**Song repeats note "G" followed by "D"

Is this how the is intentionally played? Or is it some glitch?

Thanks!