The person has to run in the direction of the bus over some distance after getting down from a moving bus due to the concept of inertia.
Inertia is the tendency of an object to resist changes in its state of motion. When the person is inside the moving bus, they are also moving at the same velocity as the bus. When they get down from the moving bus, their body still retains the forward velocity it had while inside the bus.
Since the person is no longer in contact with the bus, there are no external forces acting on them to slow them down or change their velocity instantly. Therefore, the person continues to move forward with the same velocity as the bus had at the moment they got down.
To match their velocity with the stationary surroundings, the person needs to exert force in the opposite direction (towards the bus) for some distance to gradually slow down and eventually come to a stop. This is why the person has to run in the direction of the bus over some distance after getting down from a moving bus.
I hope this helps! :)