Not here to answer, but to provide some context to this question.

I believe OP is referring to Liangzhu jade like this one: 反山 M12:98, it is 10cm tall; and here is the details, the scale at bottom is 5millimeter.

I don't know how jade carvers did it, but the lines should not be indistinguishable to the naked eye.

The human eye can distinguish two human hairs lying side by side and human hair is less than a 0.1 mm think.

For reference the thickness of a US nickel is just under 2mm. If you look at the edge of a nickle you will be able to distinguish small features such as scratches and nicks.

So these lines should be clearly visible in bright daylight.

Did they have any kind of lenses in ancient China? Even like pinhole camera type? If they did could that explain it?