1 possible path for the 15kV fault to shock this man would be if the guy is a path between the grounded light socket and the metal plumbing. I could see where the light's grounding connection to earth is actually done back at the main service panel, but the plumbing pipe could be in the ground closer to the fault so the physical distance between these two ground points could produce a voltage.
I know that at electrical substations several ground rods are use as well as a ground grid buried under the whole site just to limit the ground potential rise between two points during a fault at the station.
Andy
