I believe the Economist is using the wrong term here, right? "Trans X" means "Was assigned another sex at birth, but feels like an X and wants to be called an X" I think, at least.
Yes -- that made the article instantly unbelievable. The person in the first paragraph is a boy, not a girl.
The entire premise seems rather shaky. The benefit to trans surgery is that a person can live their life; the downside is that sometimes the diagnosis will be wrong. But we can apply the exact same argument to every single big choice in this world.