Also, dithering and color quantization are two vastly different operations on two different data types in two different domains that don't belong in the same topic at all.
Still, color quantization is a really interesting rabbit hole to go down if you're new to graphics programming, or at least it was for me. It's a mixed blessing that almost nobody has to confront the problem anymore.
Really? Dithering is generally only useful with quantized colors, you can't dither something that's already quantized without knowledge of the original, and many/most people who want to do quantization also want to do dithering. The algorithms themselves might not be conceptually similar, but for practical purposes they seems very related.