[TeMPOraL]

FWIW, Great Filter is a really simple idea, and it's very well known in certain circles (e.g. LessWrong community, to formation of which Robin Hanson contributed). I personally had no idea Robin coined it, or that Bostrom wrote about it, despite reading some text of both - and yet I could still give the same explanation way before Kurzgesagt's video aired.

Which is to say, I didn't find the lack of attribution worrisome in this video, because the idea is pretty much "public domain" in the circles interested about the future. It was (as you note) before the time when Kurzgesagt decided to get super-thorough about citing their sources, and I charitably assume that the authors of the video were just aware of the concept of the Great Filter, and not necessarily where they learned about it from. It's a simple idea, easy to explain, and easy to make inferences from - so it may not have occurred to them it's worth tracking down who originally coined the term.