A person sitting in a moving car will have a form of energy known as potential energy. The reason is that the body is at rest, even though the car is moving. Potential energy is a form of energy possessed by an object at rest.
When you sit in a car, you are not using the energy stored in you to make the car move, but rather you are moving with the speed of the car. On the other hand, the energy possessed by a moving car is known as kinetic energy. It refers to the energy possessed by an object because of its motion.
However, if the man decides to alight from the car and start moving towards any direction, the type of energy he possesses will no longer be potential energy but kinetic energy. Similarly, if a moving car stops, both the man and the car automatically have the same form of energy (potential energy).