For the animal to get shocked it has to complete the circuit between the hot wire and the ground. You install the hot wire on insulators to keep it electrically isolated from the ground. In your set-up the soil will be the ground but so will your metal fencing.
It would be interesting to see the write-up about those sketches so I'd better know what they are trying to show. I think what they are trying to show is that the grounding rods need to be far enough away from the piping going to the metal water tank so the tank is not part of the grounding system. But that "poor' sketch shows the electrified fence close enough to that metal tank so that a cow can touch the hot wire fence and the grounded tank at the same time. As long as the cow is not close enough to the hot wire to touch it she can't complete the circuit.
Your buried wire will be part of your grounded system, it should be. As long as the hot wire is insulated from the grounding system it should not short out. Did you get this from Premiere1? Call them and chat about it.
I will point out that this shows how to not shock your cow when she is getting a drink. A shock is what you want to happen if a predator touches a hot wire.