I mean maybe it just reflects that gender is contextual performance, and in some parts of our lives we were performing for the audience and some parts we're performing for ourselves.
I changed my name around the same time I started openly identifying as genderfluid, and even though I treated them as separate journeys they intermingled a lot. I have no problem referring to that earlier version of myself (to whit: I already refer to that era in the third person like another entity rather than a deadname, per se) as a "boy", but explicitly BOY: he was young and naïve and ignored his genderfuckery and a lot of other phenomena that have since come to define me.
I also think (and I've heard this from several other nonbinary folks of various flavors) there's something fluid about youth that is expected to become rigid and playless (antonym of playful that I just made up but should probably use somehow...) that is not available to "men" and "women". Gender constructs are socially prescribed, and I've often felt that cultures who are more rigid about binary genders are creating the need for third genders, whereas if a culture allowed for a less rigid spectrum some portion of trans folks may just be able to vibe within those broader, more flexible categories.
TL;DR: a culture can have a finite number of genders or it can have rigid gender boundaries, but it cannot have both. I envision this as a giant, flexible tent held up with two poles vs. an estate with two locked mansions and thousands of tiny houses being built on the lawn.