That is not Kion. It's Nala's father, Kion's grandfather, when he was a cub. And you did not watch the whole thing. Kion's grandfather did fall from a big branch. But he was saved by the Lion Guard of his day.
Though only shown in Rafiki's painting as a cub, Nala's father had gold fur with light yellow paws and underbelly, a white chin and a red tuft of hair on his head and a tuft of red hair on the tip of his tail.
His appearance in this painting bears a striking resemblance to Rafiki's paintings of his grandson Kion.
Prior to The Lion Guard
Sometime during his childhood, Nala's Father fell down from a tree branch, but was rescued by the Lion Guard of his time.
Upon reaching adulthood, he met a lioness and had a daughter with her named Nala. What happened to him after this is unknown.
Nala's Father is seen as a painting on Rafiki's wall. Beshte points out the curious cub to Bunga, and the pair mistake him for his grandson, Kion. As Bunga taps the staff on the image, they watch with horror as he plummets from the tree. Unable to handle the outcome, Bunga removes the staff which prevents them from seeing the final outcome.
Later on, however, Rafiki reveals that it is in fact Nala's Father who, when he was a cub, fell from a tree but was saved by the Lion Guard of his time. He shows the modern day Guard the whole event by finishing the whole animation.