It's really hard to assess the rates of a societally-abhorrent psychological condition because most people self-censor. The Amsterdam Gender Identity Clinic has documented a twenty-fold increase in the number of people coming for treatment, and although the fraction who end up on HRT has dropped from 90ish percent to 60ish (I forget the exact numbers--you can look up the paper if you're curious?), the rates of reported satisfaction and continuation with surgery once having stayed on HRT for the requisite time, etc., has stayed constant. It's very solid evidence that either (1) some societal or environmental factor is causing WAY more people to have significant gender dysphoria, or (2) as stigma decreases you find that, gosh, a lot of people were afraid of the stigma, and the rates were drastic underestimates before.

So I am very doubtful of the 10,000 number (I'm assuming you're talking about the U.S., given your later reference to 4.5M "Americans"). It seems an extrapolation from older studies.

However, it isn't clear to me that the late-onset around-puberty gender dysphoria phenomenon is fully explained by a welcome release from paralyzing social stigma, especially at the upper limit of the frequency that people report (which from what I've seen is lower than what you claim activists claim, but still surprising). This is a change in frequency of several hundredfold at least, which starts getting hard to explain with stigma because who-cares-what-you-think contrarians are more common than that. Your alternative hypothesis of a social-media-induced fad is worth scrutinizing, as are other hypotheses.