The code you saw in the video uses Tailwind CSS, which means the code doesn't generate a class for `text-gray1`, but rather, it creates a simple tailwind.confg.js file that lists out all the colors (and every other design scale like typography, spacings etc.). Tailwind uses this config to generate all the functional CSS classes necessary. It is highly suited for building custom UI designs, unlike Bootstrap, Bulma etc. that brings its own styles.
The software also can generate BEM like you wish for in the future. One of our earlier iterations did do that, but the default stack today is Tailwind which I've found to be the second best way to approach CSS (the first is CSS-in-JS, but with explicit design scales).