Not necessarily. My niece is an excellent gymnast and loves it, and it's the only sport she's ever done. I imagine when you're one of the best at your activity you tend to enjoy it more.
Probability dictates that there are people who find their passion with limited guesswork, and hopefully your niece is one of them. If a major part of enjoyment of a sport is how good you are relative to your peers, however, that is unlikely to last. AFAIK gymnastics has a very short timeframe for most women to be competitive as well, exacerbating that fact.
Only recognizing your own talents is more than random probability, and can be achieved at an early age for the truly talented. It's not hard to imagine that those who are legitimately talented be it in art, athletics, or academia, take pleasure in their activities not only for the competition, but in witnessing and experiencing the progression of their skill.
