I mean, he thought he could reject an identity being forced on him against his will. He thought he could point out that one of the characters in his book was born a boy.
Poor, naive fool.
He needs to understand, that henceforth, when he is referred to as cis, it is in the context of 'not being a woman who identifies as a man'. He needs to understand, like women, that he will always be known as 'not' a (insert opposite sex here) who identifies as something.
He can never be a concept, an entity, or an example of material reality in his own right, ever again.
He can only ever, for the rest of his life, be referred to in the context of trans.