So, it is correct to refer to “natural family planning” as “birth control” then?
Of course. In fact, properly speaking, NFP is the only true form of birth control, because it allows for birth and requires control. It is not, however, artificial contraception, in that, it does not actively work against conception in an artificial manner. That's the moral difference between then two for Catholics.
Yes, NFP is birth control, inasmuch as it is a way to either postpone or achieve pregnancy through knowledgeable COOPERATION WITH natural fertility patterns. But it is not contraception, which means acting AGAINST natural fertility patterns.
There are some non-Catholics out there, including the crunchy-granola subset of feminists, who like NFP because it does not pathologize the normal functioning of female physiology, nor treat a fertile female as if she were diseased.