This is where you have to start when you read b/s articles like the one in OP.
But, to answer your previous question, lets first look at a different example: the word "car". Back in the days, before we had horseless carriages, "car" was, basically, a contraction of "carriage". I.e. two hundreds years ago it would be completely natural to picture cars as being pulled by horses, and cars that weren't pulled by horses or other beasts of burden would be the stuff you find in fairy-tales.
Were English speakers stupid two hundreds years ago to so grandly misuse the word "car"? -- I don't think so. In their context it made it perfectly fine. The context is gone now, so, whoever calls a buggy with a horse a car today is not using the language correctly.
And such is the case of the early filesystems. By today's standards they wouldn't have qualified to be called that way. Probably, the early filesystem more closely resemble key-value stores we use today. The discrepancy happened due to semantic drift caused by changes in technology.
Similarly to how you wouldn't use the word "car" to describe a buggy today, you shouldn't use the word "filesystem" to describe a key-value store today. Well, unless you make sure the readers understand that you are talking about what happened some 50-60 years ago.
And people who get to decide what to call a filesystem and what not to call filesystem are the people who make filesystems (and I'm one of them).