This "coupling" BS is just a way to rationalize water in boxes and other real ground faults.
Greg it is not BS, it is a real issue.
As a an example when you wire a line isolation monitoring panel you should not even use THHN/THWN at all as its dielectric strength is to low.
Now I fully understand that LIMs are more sensitive to this than a GFCI but the cause and theory are the same.
Now instead of the LIM take a less sensitive class A GFCI and run a couple hundred feet of circuits on the load side of it and you may have a real problem.
If you are interested in some more info read the linked article.Impedance of Wiring on Hospital Isolated Power Systems used in Operating Rooms
Another example of capacitance coupling can be observed when testing the continuity of long cable runs with a good meter. You will get an ohms reading until the cable (capacitor) charges.