yeah it isn't the normal icon for Apple Music on our devices.....but you can test it......it appears to add the song to your music library. It doesn't stick it in any playlist, just adds it. Also, if you already had the song loaded in your library, but maybe from a CD you ripped, it adds the Apple Music version also, so now you have it twice.
The thing that's confusing to me, there's no way to "like" or "dislike" a song with this interface. I've asked on this forum last month whether Spotify has a like dislike option on the Tesla interface, no one answered. Seems strange to me, but we'll have to see how this develops in the future.