Devil's advocate: it's probably not due to the "download apple music" button and more to do with the tagline that came with it: "Millions of songs. All ad-free. New users can get upto 3 months free.".
Good thing Google's feedback was so specific that they know exactly what they did wrong and how to fix it /s
The next line is "if we told you what crime you're accused of, criminals would abuse that information to evade the law"
That’s the first time this is an issue after 4 years being on the Play Store and immediately they remove the whole app.
is the tagline part of the webview, or is it content controlled by you, and the webview only opens when you tap the button? if it's the former then I'd agree it's not an ad, although I can still understand why it might look like an ad to a reviewer who doesn't understand the nuances.