The problem is that they could do some damage to the user even in perfect good faith. Just think about someone who listens music at unusually high levels or with channels heavily unbalanced compared to someone with normal hearing abilities. That innocuous information if leaked could hurt the user insurance or job opportunities.

I have no idea if their app collects this information too, but it's just a matter of time before someone becomes interested to it as it happens with any kind of data that can be used to profile people.