Source for Apple Music being an electron app?
There is a Apple Music related preference pane that is a webview but that is not the same thing.
I just checked since I own multiple macs. It's true, they're going away from webviews, but their new native app ui is broken! When you go Browse, click the first big image and then press the back button in the top left corner, the white navigation bar space at the top disappears, causing the content below it to visibly jump up.
Sigh.
...probably some APIs used that don't work on older OS's, and/or why bother supporting old Macs when the old app still works fine? I don't think it's a big deal.