It is a complete answer. Thomas wasn't allowed to compete in the women's category because "women" refers to gender. Thomas was allowed to because the rules specify how to qualify for the category, and Thomas meets the requirements of those rules at the time. Those exact same rules could be used regardless of the label for the category. Conversely, the NCAA has
updated their rules and now Thomas would no longer qualify. They did not need to change the category label to exclude Thomas. They needed to change the rules.
Your confusion is baffling.