"Just kidding, I've been very athletic all my life"

Kiana Tom is likely making a joke about her athleticism. She is implying that she is not as sports as she shows up, yet is in fact rather sports. This could be a method of her downplaying her own abilities, or maybe a means of her showing humbleness. It could also be a method of her sharing her satisfaction in her athleticism. Whatever the case, it is clear that Kiana Tom has actually been involved in sports for a long period of time. She likely has a lot of experience in different sports and activities, and takes pride in her achievements. Her quote is a way of her revealing her satisfaction in her athleticism and her capacity to remain energetic throughout her life.