The best statement describing how this demonstrates Newton's third law is: "The trampoline pushes back with equal force but in the opposite direction."
This illustrates Newton's third law, which states that for every action, there is an equal and opposite reaction. When a person jumps down onto the trampoline, their weight exerts a downward force on the trampoline, and in response, the trampoline exerts an equal upward force, propelling the person back upwards.