> background playback, audio only mode
https://developers.google.com/youtube/terms/developer-polici...
> You and your API Clients must not, and must not encourage, enable, or require others to:
> separate, isolate, or modify the audio or video components of any YouTube audiovisual content made available as part of, or in connection with, YouTube API Services.
> promote separately the audio or video components of any YouTube audiovisual content made available as part of, or in connection with, the YouTube API Services;
> create, include, or promote features that play content, including audio or video components, from a background player, meaning a player that is not displayed in the page, tab, or screen that the user is viewing;
The author blatantly violated YouTube's developer policies then complained that YouTube was upset? Why the victim complex? What did he expect? He's lucky they didn't choose to go down the lawsuit route instead.
This doesn't seem like an arbitrary policy either. If he's playing the video where the user can't see it, the user can't see ads. If the user can't see ads, the video creator doesn't get paid.