I think they are conflating a lot of things in an attempt to justify their preconceptions, which is nothing new.

First of, GC rejects the notion that to "exhibit masculinity" means anything other than labeling behaviors anyone and everyone can and on occasion probably participate in. There simply is no refutation of this. Every man and women exhibit masculinity and feminity. People just choose what they observe in putting labels on people. If I like things others label as masculine or if I behave in a way others label as masculine, does that say more about their label than it does about my behavior? It really says nothing about me than I'm someone who behaved in some instances in a particular way. Extrapolating anything bigger from that about me, to put a label on me, denies the elasticity of our minds and how our ability to adapt to circumstance allows us to behave in infinite ways. It also intentionally ignores the times I would behave in ways contrary to "masculine". It is filtering the available data and focusing not on all of what is there but instead on what they want to see to draw the conclusion they want.

Is an identity that is somehow gendered separate from one's measurable and empirically observable sex (either before the surgeries or through some other means), or not? In addition to taking a tragedy some kid suffered and turning it into some sophistic talking point, they instead seem to be spinning a loss for their sophistry into win. Did the person come to realize their actual sex, or did they discover their so called "gender identity" which can not be proven to exist? Before they can make any of the conclusions you credit them for making, they have to show they have validly ruled out that the person came to know their sex instead of came to know their gender.

As for your last question, I can make no leaps. I need certain definitions for words, and then upon receiving real and workable definitions (if such exist) I will need additional things defined and clarified. Anytime we attempt to overthrow established ideas or established science (of sexual reproduction) and the language describing them, we need put their proposed replacements (reality's replacements) on a firm footing, if possible, or we have to reject it. What is "trans" with regard to sex and with regard to gender? What is gender with regard to how we define and classify humans based on their observable physical characteristics? What is sex with regard to how our species (not clown fish) reproduce? What is a person's own identity as a separate thing from their physical characteristics by which we can identify them? Why is that personal, stated and not empirically observable, identity considered fixed or treated as if it were fixed when our sense of our self is always changing as we learn more about ourselves and our place in society?

If anything, I think our sense of our own identity is more like an alias we use to accept our place in society or to create a place in society we want to inhabit-- like when a kid moves to a new town and they create a new identity for themselves to be cool. Since these things are socially constructed by society and by our culture when then our brains find the nexus of them all to create a sense of self (which is probably one of many), and since society and our culture are constantly changing, how is giving an external name to an inner sense of identity not like trying to grab the wind? How is trying to cling to a momentary sense of identity not making it static and stiff and cumbersome and, regardless of how well it may have seemed to adapt to some specific moment in time, how is it not at least partially stuck in that moment unable to move forward? How will clinging to an identity not make you topple over metaphorically instead of moving forward with time and with the changes that always come and are ever in motion? I reject trans ideology and 'queer theory' and all the ridiculous ideas that come along with them, but I welcome an honest a rigorous attempt to change my mind-- not red herrings and bad rhetorical tricks.