Really long-range artillery is miserably imprecise, with Circle Error Probables (CEPs) somewhere around a mile or two at max range. With enough rounds, they can hit Seoul, somewhere - they just can't pick where. It's useless for attacking military targets at long range because they would have to fire way too many rounds to get any effect.
On the other hand, we are very good at finding them. We have counterfire radars that can locate where rounds were fired from very quickly and have a round go after them while their round is still in the air.
The author did not invent those terms. They date at least to the 1950s (or '60s) regarding the use of nuclear weapons against civilian, industrial, and infrastructure targets (countervalue) or against troop formations, airbases, naval harbors, and the like (counterforce).
Any such artillery employment is going to be in the face of nearly immediate ROK/US air supremacy, including 24/7 armed drone surveillance on station. 30 minutes into the war they won't have any major stationary launch sites left and probably no airfields either. Mobile launches are visible from space. Nowhere to hide.
I wouldn't try it, but then I'm more or less sane. Dumber things have been done, I suppose...