There’s a video going around of a guy using a useragent spoofer to prove that it only does this on non-Chromium browsers. So I don’t think it’s necessarily anti-adblock, but it could be interpreted that way when you consider Google’s plans to implement DRM in Chromium.

When I went rooting around to find it. I figured it was some QA process that starts 5 seconds after the video loads (the timer seems to be async and the code sends a promise off while it waits). Of course, it’s all minified JS so it’s a huge pain to read.