Now, I'm not too caught up on the rhetoric, so maybe I'm incorrect here, but I never really saw "Femboy" as a transgender thing, and more of a kink thing like someone who identifies as male dressing up as a woman, or wanting to be talked to like a woman, while still being male, and under that parameter, it doesn't shock me that its the more popular search, at least it seems like it is from the graphs.
That said, I am surprised that on the list of metro areas, Minneapolis and Sioux Falls are so closely matched.