BTW! That's EXO's OVERDOSE MV
That might be a comparison between the Korean and Chinese version?
This was never a feature, that's just how the video currently playing looks.
I thought picture in picture was a thing on Android TV since Nougat. In Live Channels I think you press OK to bring up the menu and PIP will be in there somewhere. I'm not sure what apps are actually supported though.
If you look at the images, they appear to be from a music video, and the same one at that. Could it be the video itself just looks this way?