Most of our existence is what it is because it has been defined into existence in some legal legislative action, academic dictionary, or scientific or legal journal or and these terms have been accepted by the scientific and legal communities. This is especially true of this gentleman's profession. Transgender, gender identity, heterosexual, male, and female and as well as definitions of all of the attributes of each exist within the scientific and legal literature so for practical purposes have a reality. If all legal and scientific literature were to go poof and vanish from existence then our very conceptual existence would vanish also.
This man must be an idiot for not knowing this. Transgenders exist because we exist and the scientific, medical, and academic community in some part uses the word transgender to label our condition so all of those concerned can communicate about us.
One individual cannot define us out of existence because of his prejudices because one individual by himself or herself can not create an academic language. One individual can contribute his or her definitions of concepts to their academic community, but the the community as a whole has to accept and assimilate these definitions for them to mean anything.
When one is in grade school, high school, and undergraduate school one is taught that the world is as it is. When one goes on to get a master's degree one learns that the world is as the PHD's within the academic field define it and the legal system has legislated it into law, rules, and regulations.