I'm not sure I should share my secrets now lol. But the answer is linux. I haven't tried screensharing before. But I have tried with other DRM stuff and it got blocked. So I wouldn't be surprised if this was a fluke. Definitely makes making memes easier though.
If the video quality is low enough then Netflix and co don't bother. It also varies on who is the content supplier, some are less fussed about protecting content that doesn't bring in much money.