Nature can be a pretty harsh place. You have to fight for your territory, stand up to predators, even if they are ten times your size. And you have to be fearless. And this turtle definitely was. It's not something you see every day - a teeny weeny turtle standing up to two enormous lions. You'd worry that, oh no, this will end in catastrophe, but amazingly, not only does nothing bad happen to the turtle, it managed to chase the lions away from its waterhole.
Maybe it's because lions are just large kittens in disguise, and they're nicer than they seem. Maybe it's because they know how resilient turtles are and that turtles can easily outlive them in the wild. Or maybe, it's because cats of all sizes know, through the experience of their own species, that one of the fiercest wild cats in the world is a tiny kitten, so tiny doesn't mean not ferocious.