I didn't explicitly see anywhere in the article that binary sex is a colonial construction. I realise that's a concept that is repeated often by TRAs though.
It is awful how the British Empire persecuted indigenous cultures and undermined their traditions. It's a common theme in colonial history. As I understood it, the hijras were a wealthy class. They had a lot of property and therefore power. And their inheritance and wealth was passed down through adopted children. So to undermine this, I think the British decreed that inheritance could only pass through biological family ties. So it obviously affected the hijras more than anyone else in Indian society.
That said, biological sex is not a colonial or imperialist construct. Patriarchal societies such as the ones in India do not openly accept homosexuality or allow men and women to deviate from rigid gender roles.
Men who are very feminine or who wish to have relationships and families with other men have to switch to another gender category, such as hijra, to be able to openly live a very feminine life. And these third gender roles also have strict boundaries. So Indian men and women aren't allowed to be who they are or dress / behave as to wish. If they deviate too far from the norm for their gender role, they are only accepted by patriarchal Indian society if they go into another box. Males who do not conform to the masculine gender are not allowed to be men.