As the video explains, a downed high voltage power line can energize the surrounding ground (or any base especially if moisture is present) that has electrical contact with the wire directly, or even indirectly through something like a metal fence. This high voltage charge can create a lethal hazard for over 30 ft depending on conditions. The electrical energy travels in "rings" like circular waves/ripples from a rock thrown into a pond. You don't want one foot in contact with one ring and your other foot in contact with another ring. Those invisible "rings" have an electrical charge between them. This is why you keep your feet close together and shuffle away. This prevents your body from "short-circuiting" two rings through your legs. Even firefighters will stay back until the power company isolates the power lines.
I hit a power pole before and I stayed in the car until they disconnected the power from the power pole and they say that it is safe to exit the car and I know ok?