I'm not going around saying women should be called menstruators, but when differentiating between women who do and don't menstruate, it's a useful shorthand in that specific context.
The problem is that if you are trying to analyse the effect on equality, (which this article does) you create a false distinction between women who do and don't menstruate.
If I have missed large amounts of school because of periods, that doesn't suddenly become irrelevant because I become pregnant, or even when I go through menopause.
It creates a false impression that periods are a niche phenomenon that could happen to anyone, when most women menstruate.
By avoiding the term 'women' they are also swapping one taboo for another. They are endorsing the idea that biological sex, specifically female biological sex is shameful and distressing.
They don't have the same qualms about the male sex.