But once you divorce sex from reproduction, it all makes sense. Once you realise sex is nothing to do with reproduction, except epiphenomenally, and is all to do with chromosomes, cultural influences, genitalia, hormones and cishet white supremacy and the colour of children's toys and clothes, then there is no reason not to define sex as anything you like - or anything at all, whether you like it or not. Sex is club, a friendship group, a way of pleasure, a mark on a passport, an identity or series of identities of differing degrees of marginalisation.
As the article says:
In science, how sex is defined for a particular study is based on what organism is being studied and what question is being asked. The criteria for defining sex will differ in studies of mushrooms, orangutans, and humans. It will also change if the purpose of the study is to look at genetics, or gross anatomy, or hormones, or reproduction, or gender.
Or, you can be, like, totally out of date and unchill and think sex is all about reproduction.
On another note, I see they have provided a reference list, but have not thought it worthwhile to cite the references in direct support of their claims. I suppose it's generic "further reading". They also seem to be working on a loose definition of the term "definition", including "marker", "associated characteristic", and (in "assigned sex at birth") "term I just made up" which doesn't reflect any reality on this planet.