That doesn't clarify anything. What's a "premium" streaming app? Why doesn't (or didn't) Spotify, who publicly opposes the 30% cut, qualify?
No official source qualifies and the article you linked just guesses based on screenshots. It also tells you that Apple does take the 30% cut if you trick the user into not realizing there's an Apple tax.
The video I linked (I know, it's long) discusses limitations as decreed by Apple itself. There's another video on that channel with even more in-depth information from Apple. There's no offer to make a deal and become a "premium service". I'm sure these guys would love to get their app available on more platforms, providing more value than they already can with just smartphone apps.