Rendered Image Denoising
Your link is to paid course :) In ray-tracing too few samples will generate something like at the top  In fact the link with the picture answers your question https://chunky.llbit.se/path_tracing.html

2) Ray-tracing is hard... but not impossible, google for "python ray tracing module"... But something looking close - easily https://stackoverflow.com/questions/22937589/how-to-add-noise-gaussian-salt-and-pepper-etc-to-image-in-python-with-opencv Although actually on the ray-traced images the noise can change because of slope and environment.

If you still want ray-traced noisy images, better to find tutorials for 3D modelling programs, like "ray tracing in 3D Studio MAX tutorial"