Only making the connection of the AC neutral and AC ground at the source. Yes the AC ground(green) is connected the boats DC ground, but the AC white (neutral) is not connected to the boats DC ground.

This is not the same as household wiring practice where the neutral and ground connect at the receptacles even though they each have seperate paths back to the source.

In Wings example on pg 164, he shows that with the White and Green connected at the boat, resistance in their return path(or a break in white and green) could open a less resistant path to shoreside ground from propeller(connected to DC ground system) through the water to land.