Scout2016 this is one of the problems stemming from the wording of the 2010 Act - it says "A person has the protected characteristic of gender reassignment if the person is proposing to undergo, is undergoing or has undergone a process (or part of a process) for the purpose of reassigning the person's sex by changing physiological or other attributes of sex."
Within gender ideology, 'attributes of sex' has come to include men wearing a dress, make-ups, heels etc.
The terms non-binary and gender fluid are, I would say, almost the opposite to gender reassignment (if you're non-binary or flit between different gender identities, what on earth to you transition from and to), which did in the 2010 EA acknowledge the reality of there being two sexes.
But ten years of gender ideology has made us lose sight of that.