You: "Trans is always about stereotypes."
The doctrine of gender identity connects embodying the sex stereotypes and sex role stereotypes of the opposite sex with (trans)gender identity. When a person who is male states they identify as a woman, this is not and it cannot be based on knowing what it is to inhabit a female body or what it is like to be born female in a male-dominated world. They are however using the word woman as a referent. (A referent is the word we use to refer to a living being, an inanimate object, a location, an abstraction or an idea.) In this case the word woman is a stand-in for everything that this male individual believes makes a woman. We know from countless autobiographical works, videos and self-reports that in the absence of knowing what it feels like to inhabit a female body, this belief centres on the sex stereotypes and sex role stereotypes associated with being female and with that individual's strong preference for any number of those stereotypes.
Which is why training courses delivered by transgender organisations focus on stereotypes when explaining what it is to have a transgender identity.
Me: "Here are examples of when it isn't."
That study does not disaggregate its data to allow for such an absolute statement. It lists various categories of stereotypes, but it does not tell us whether even one of its study subjects rejected all the stereotypes associated with the opposite sex. It doesn't even mention in passing whether a study subject who has not adopted one stereotype of the opposite sex is more or less likely to also reject other stereotypes, or whether those who haven't adopted opposite-sex stereotypes always embody the stereotypes of their own sex instead. The study authors also fail to disaggregate the data by identity, i.e. those children who told them they do not identify with their own or the opposite sex or who identify with both are subsumed into the transgender group. So we cannot tell whether stereotypes are more important for those who do identify as the opposite sex and less important for those who identify as both or neither. The study only mentions that some children adopt some stereotypes of their own sex, but says nothing about how these same children feel about all the other measured stereotypes. And finally, if a child were to believe they are the opposite sex because they strongly prefer just a single stereotype associated with the opposite sex, they would still be basing their belief on stereotypes.
The authors don't actually mention tomboys in the body of the study, or the conclusions, so I'm not sure why you are so adamant about that word. It only appears in a brief literature review at the beginning and the connected references at the end. Instead the study states that like all children, those who identify as trans embody some stereotypes more strongly and others less strongly. As femininity and masculinity do indeed exist on a spectrum, and we all fall somewhere in between, this is entirely expected.
You: "Trans is always about stereotypes even when it isn't."
Do you understand what class-based analysis is? It does not depend on all members of a class meeting all of the described characteristics to be valid.
I do believe that you'd be better off directing your ire at trans rights organisations and campaigners, who have been pushing the connection between (trans)gender identity and stereotypes for decades now. I would welcome a return to the previous understanding of transsexualism and gender dysphoria as a type of body dysmorphia, but I won't hold my breath as this does not seem to serve current aims.