Especially odd given the entire point of Widevine is to set a content protection minimum that works cross-platform, which his machine obviously meets given it's playing video (while I had suspected xFinity would require Widevine L1/a full hardware chain for any playback, it looks like they offer a lower resolution like 720p(?) for L3 devices).

My cable box still outputs upresed 720p so I’m not too sure what they’re protecting.

I'm not sure if that's actually the case here, but it's hard to tell if the image in the article is just a sharp 480p image or 720p. It's up to the streaming service to decide the quality levels provided to L3 streams.