It is about dehumanising menstruators because they are not catered for properly at festivals. They don't seem to have noticed their own dehumanising language.
The erasure of any mention of women and girls and the replacement with the words menstruator and people with periods is the dehumanising language. It is being used to describe women and girls even when they are not menstruating, as women and girls who are not actively menstruating at this moment but have to plan for their periods are affected, girls who are not yet menstruating will be affected in the future and women who used to menstruate have been affected in the past. This means that they are not using these words to describe someone menstruating, but as words to describe our sex class. They are using them with the same meaning as the words women and girl have always meant. Its use in this way is an illustration of why we need words to describe a human sex class, but apparently the words we had are not OK and we have to use bodily functions to describe that sex class instead.
I know we have seen this to many times before, but it is so stark in this piece.
BBC: It's time festivals catered for people's periods
By the way, the title on the clicky link is what you see on the home page.