What is "SoC" here?

And "cells of different max capacity will get different SoC after same mAh used". But the smaller capacity battery is not giving as much currency as the bigger one, I think?

I am thinking of analogy of two water buckets, another one larger (mAh) than the other, but both have the same water level (voltage) and the level is at the same height (voltage). Both have same diameter (resistance) tube underneath going to the Y-connector and then the connecting tube is leaking water (current) out to somewhere.

I think, the buckets will be empty at the same time, and still no water is going from the larger bucket to the smaller one. (or there is an error in my thinking?)