Trumpy, you will find "ground" is not really "zero volts" from point A to point B. That is why we have ground electrode systems, article 680 and in this case 682. Once he establishes his equipotential plane and attaches it to the equipment, hence the EGC, everything will be "zero volts" again.
This is simply the consequence of using the earth as a return path for circuit current. I know we say that is not supposed to happen but current takes all paths and that grounded PoCo transformer shares the earth with the grounded service drop conductor. The grounded transformers on L/N transformers also share earth with the grounded conductor going back to the sub station.
Current is flowing through the earth all over the place and there will be some voltage difference between each ground electrode along the way.
To see this, all you have to do is look at the current flowing in that #8 coming down the pole.