Confusing Barrio Color Scheme Settings UI Labels

Barrio colors are based on Material Design color managent, using Bootstrap framework.
The theme generates site colors based on 2 colors
Please refer to https://m1.material.io/style/color.html#color-color-system

I read the page you linked to. It does not have the word "base" on it anywhere.

Let me reiterate my question: What does "Base color" refer to? We don't have the option to set a "Base color" in the UI, so where does the value come from?

Primary color

Why is there a different choice for "Base color" and "Primary color" in the select list if they are the same? It's very confusing.