I took an evening to read and watch some Rippetoe lectures before I made this response, in the anticipation of some SS acolyte taking issue with it. But Ripp is at least partially responsible for this ''hamstrings are super important in the back squat'' idea. And the following passage is about as close as he ever came to outright saying that the hamstrings are a prime mover in the back squat.
https://startingstrength.com/articles/squat_rippetoe.pdf
Most of his argument about why people should lowbar squat is all about the hamstrings. It's about ''recruiting the most amount of muscle possible.'' What muscle is ''not recruited'' in the front/high bar positions? Well, the hamstrings, according to Ripp. And what, according to Rippetoe, do the hamstrings do in the back squat? ''open the hip.'' Later, in the 3rd edition of starting strength, he seems to admit his error in stating that the hamstrings involvement in the back squat is isometric (he never admits that this is their function in the front squat as well, essentially nullifying the whole argument from the get go), and he even states in the lecture provided below that the hamstrings cross two joints (and thus resist knee extension). However, he continues to overemphasize the hamstrings involvement in the squat to this day. He keeps his front squat/low bar argument basically intact but he just doesn't follow it to its conclusion.
But, if you're an educator, as Rippetoe is, and you spend all this time talking about the hamstrings involvement in the back squat, it's going to happen that some of the people you educate come away with the impression that the hamstrings are prime movers in the back squat. It's not for nothing that Greg's first attempt at his article was met with extreme skepticism. If you look in the comment section of the related video, someone even calls the squat a ''leg curl.''