Point of order - non-binary people sometimes medically transition. We might not choose all the options to swap to a full binary presentation but target things which cause us duress.

Non-binary is under the trans umbrella though not every Non-binary person identifies as trans. There are political enbies or people who see their ambivalence towards gender and sex characteristics entirely as being an expression of a Non-binary experience while others experience the same euphoria/dysphoria to their natal sex characteristics that binary trans people do but desire more of an absence of all sex characteristics or a mix of male and female phenotypic traits.

Your statement in effect only describes a fraction of Non-binary people.

They could be. Transitioning doesnt stop them from choosing to identify with a non-binary gender.

Are you thinking of intersex? Even in that scenario, I don't believe that statement applies.