I like that the author came to the idea by cross pollination via web components.

However, it's basically describing the "modifiers" part of BEM, which is a pattern that emerged from structuring CSS. Neither custom element or attributes are needed, even though they might feel different.

If you like that kind of pattern to structure CSS, then combining it with custom CSS properties (often called "variables", example: --block-spacing: 2rem) makes it even more modular. These properties follow the cascade rule.