Yes. CSS is, simply, objectively, not a programming language. It is not for writing programs.
That doesn't mean it isn't worth developing expertise in. Lots of technical subject matters are not programming languages.
> Surely it’s a coincidence the first group tends to be more male than the second.
I'm starting to suspect that what the author perceives is more about how seriously people take the author, rather than how seriously people take front-end development.