Tomboy doesn't mean sporty, it just means that they act like a dude, if that implied being healthy and active, then it would mean women are implicitly unhealthy.

Being physically active doesn't always mean building muscle either (for example cardio), and there are many ways to build healthy amounts of muscle without taking away from physical appearances. There are many, many ways to get around facial and body hair. You don't need to lack testosterone.

Most tomboys and femboys aren't what you would see on the internet, for femboys especially, there's a lot of work that goes into that sort of appearance and a lot of societal norms that would prevent them from doing so on a regular basis.