I don't think they made most of the quizzes either (see link in my other reply)
More likely to be some kind of color space thresholding
https://shaderacademy.com/shaders/glsl/ranked_1/fragmentExpe...
But I still stand by the ai-gen'd aspect
Most challenges were created by us, but we use LLM for example to generate comments in the code or generate some simple boiler plate.
Sometimes, it is also useful to create similar challenge to already existing one.