What other animals have a similar level of consciousness? You can‘t form the idea that you are “in the wrong body” unless that idea has been provided to you by your culture. You need linguistic and social support to even have the concept.
EDIT: Oh, you may be interested in the phenomenon of what you might call “trans” non-human animals: individuals who behave like those of the opposite sex. Apparently in some species their physical characteristics can even change, such as female lions that grow manes. But nobody is confused enough to say “trans lady lions are lady lions“; that confusion is reserved for humans. In mammals, the sex can not change. But it‘s an interesting phenomenon.
https://en.wikipedia.org/wiki/Irreversible_Damage
If you have a peer-reviewed study, that would be much more worthwhile to look at.
The layman's explanation of the phenomenon is that parents observe a rapidly onset expression of gender dysphoria in their teenage daughters which "seemed to occur in the context of belonging to a peer group where one, multiple, or even all of the friends have become gender dysphoric and transgender-identified during the same timeframe."
https://www.theguardian.com/society/2018/oct/16/academics-ar...
In my puberty I had a strong feeling of rather being a girl and this caused significant mental anguish and some self harm. If had known as much about transgender people back then as I do know I would have likely transitioned then.
Today I'm pretty okay with being a man. I still sometimes have problems with it but not in the same order of magnitude.
From these personal experiences I think it is plausible that more people transition because more people are aware of the possibility and knowing other trans people in their age. I have no idea how big that group is however.
This is an interesting case that went through the UK courts. Very analogous to OP’s situation had it happened today.
Abigail Shrier is a writer and not a scientist, and it can be clearly seen even from the title of the book that she has an agenda. The thesis of the book has been "rejected by the American Psychiatric Association, the American Academy of Pediatrics, the Endocrine Society, the American Academy of Child and Adolescent Psychiatry, and the World Professional Association for Transgender Health."
https://en.wikipedia.org/wiki/Irreversible_Damage
If you have a peer-reviewed study, that would be much more worthwhile to look at.
Interviewing parents seems like a problematic basis for an entirely new condition to me.