I just heard... Sal Buscema inks you? How cool is that? His style fits you great too. I loved his work on Spectacular Spidey, back in the day. I'll totally pick up this Black Dynamite book! Good luck with your work!
I'm gonna guess (until Ron comes around) that it's treated as a layout frame, to maintain line consistency across sequence. They would have duplicated this as a key, but not used the illustration itself. Unless they used this frame as a beauty shot that gets held over SFX/VFX, maybe with a little camera push/tilt/shake action?
Still very interested in knowing for sure, instead of just speculating.
Here's the reply I got from ~Kanta-Kun: "Actually, these are special "still-screens" that show up mid episode during action sequences. The only animation in them is usually a bit of motion/scale tweening."