I appreciate your points, but this is all settled from a legal perspective. In practice it's up to whatever cop/judge/jury is deciding on the day. We hope that society can roughly agree on things like "reasonable" and it may vary in time and space, but it's the basis of a huge amount of statute and convention, and I don't think there's anything special about music and busses that raises new questions.

By the way, you might enjoy this website which makes a fun quiz out of drilling down on these kinds of rules: https://novehiclesinthepark.com/