"Classless" also made my brow furrow when I realized they didn't mean, say, CSS components styled without a bunch of classes (a la Twitter Bootstrap) but rather, it just has no components. It's classless because it only styles some basic html elements.
That's exactly how I understood it and it sounds useful to me. No need to look up what styles do what, you can just use the standard elements and expect them to look coherent and as expected. E.g. "<header>" is descriptive enough since HTML5 introduced it.
It didn't mean that for me because we've been sharing minimal css files for decades without without calling them frameworks or "classless". Usually when you see a new term, it describes a spin on the old act. If they had also called it a "serverless" CSS framework, I wouldn't have guessed they meant that the CSS file just doesn't make any HTTP requests.
