Can someone explain to me why extinction of lions would make prey overpopulate, what about leopards and hyenas?

Pretty easy to understand. The reduction of the main predators would allow the prey to reproduce more, resulting in a higher population of prey. without the presence of predators to control the numbers, the prey would eventually overpopulate. this overpopulation would remain out of control until another predator that eats said prey comes into play. eventually, the presence of a new predator would cause the populations of both prey and predator stabilize... this concept can be applied to all predators. does that help?