Thanks for all the replies. I'm working on another piece, trying to rationalize and interiorize (...?) all these suggestions.
I am studying Helm's suggestion (among the other edits). There's at least 25+ colors on the woman's skin, and their choices and shading type led my first reaction to "color reduced cg", and the dithering does seem a bit chaotic too, which strengthens this belief. But there is the possibility that i'm wrong, and that this is complex technique.
It's hard to see order in the way the colors are chosen, he does small hue changes between main colors then adds a huge hue leap in inbetween colors , which are used in very small areas between those larger tones - by example, two large reddish areas with a line of greenish red pixels between them. Then, there are small brightness and saturation variations, but they don't follow any pattern in increasing/decreasing. The thing is that looking at it in 1x, these shifts aren't perceivable, but the final result comes together quite harmoniously. Are they necessary to achieve this effect? Probably, but how would one figure "i need more hues in the buffer colors", specially when working from reference?
These things are puzzling, and i when i figure them i will have learned, so it does help. Thx for the pointer, Helm

, and everyone.
Other people's visions help straightintg our skewed initial one.