With gender they identify what sane people would call the Anima or Animus of the Soul, every Human has a male and female part of the soul.

But they deny the soul at all because of scientism, a materialist cult build around marxism.

They then project the confused soul on their physical body, and try to adapt to it.

Sprinkle a little natural selection, self castration and gnosticism on it and there you have it.