Huge sheets: these were large high-energy physics contraptions. Full-size electrostatics (Quad and KLH) were common then, 6DQ5s were still in production, and lots of military-surplus high-voltage transformers were available.
A transformer is not needed if you can couple directly to the plates of the push-pull driver, using the Vbb and another bias voltage.
We were younger then, and full of large ambitions.
I was contrasting this situation to your case B.
Yes it can work with some high voltage push-pull mosfet or IGBT and optically isolated gate driver but is more complex than just a transformer with center tap.
I did Electrical Engineering so high voltage / high energy stuff and we had laboratories for lightning simulation tho I was more passionate about low voltage automation electronics.
As a hobby I never did projects exceeding 60Vdc open circuit the safe low voltage standard limit.
Case b) and c) where done to show that the internal plates that are fully isolated from supply have no net charge. You need to go to something like d) and then disconnect the two surfaces in order to isolate the sides with different charges.
For example the setup in Derek's test was more like
f) -| |_[resistor]_| |-
So capacitors on each side and resistor/lamp in between (that is the transient part).
So while current flows through resistor it is electrons from one plate moving to the other plate as the capacitors charge from the source.
If source is then removed and you short the capacitors all stored energy will flow back through resistor to have those plates neutral again.
So amount of energy through the resistor is directly proportional with the amount of charge being stored in the capacitors and then when they are discharged the same amount will flow back.
So electrons are the ones that travel through wire and transport the energy.
If we shield one quarter of Derek's transmission line and connect that shied on the opposite side of the resistor this capacitive energy storage will be done around the resistor so no more energy before those 65ns or so but then despite this shielding energy arrives through wires at the resistor/lamp.
And it can be DC or AC it will still get to that lamp resistor through wires despite the shield that removes the capacitive effect of the line.