Hello Stamfordman,
I agree fully with you, in that you cannot charge a non-electric vehicle.
When I issue a PCN on a vehicle in the electric charging point, I do not concern myself with whether it is or is not an electric vehicle.
In either scenario, I will explicitly refer to the type of vehicle that I saw, when writing the PCN notes.
I use code 23 when I see a vehicle parking somewhere it should not be. However, I never brought myself to using it in the electric charging point, as it is a charging point, as opposed to a parking place.