I believe they're referring to Hitchhiker's Guide to the Galaxy. It's kind of an iconic line for those who have read it because of how it sets the tone of the book: "In the beginning the Universe was created. This has made a lot of people very angry and been widely regarded as a bad move."
Parent comment is also referencing HGTTG. Right at the beginning, in fact:
"Many were increasingly of the opinion that they'd all made a big mistake coming down from the trees in the first place, and some said that even the trees had been a bad move, and that no-one should ever have left the oceans."
https://www.goodreads.com/quotes/1-the-story-so-far-in-the-b...