The article explicitly stated how North Korea might feel free to hit or try to hit places like Guam, S.K. and Japan without fear of retaliation because the author guesses the average American would be OK with losing Tokyo and Seoul but not S.F.
The part about the US absorbing an attack on a territory or nuclear umbrella ally is flimsy too. More to the point, it’s flimsier because of their “conventional inferiority.” The US actually can degrade North Korea's abilities (to put it lightly), possibly to the point of complete failure before sustaining an attack. It's dangerous for the US, but nothing like a conflict with a Major Power.
I'd expect the European countries to do the same.