They know sex is purely biological. But they introduce a word that previously only applied to language. Romance language words often have gender, but the don't have sex. Animals have sex, but not gender. But they started pushing to change the word on forms from "sex" to "gender" 30 years ago to make room for this human construct of heretofore non-existent sex classifications. Total political nonsense, and anti-science, but there you go. The radicals on the left will do anything to warp tradition for political benefit, and the sheep on the left just accept it as reasonable without questioning what they are told...and then, having gotten their marching orders, they start attacking people who didn't get those marching orders, calling them "bigots" in order to prompt the societal change their radical overlords desire.