This is tame in comparison to their normal bluster going into the US/S.Korea joint exercises.
No bluster about turning Washington, DC or Seoul into nuclear slag? No, unleashing fiery hell of the mighty North Korean people on the S.Korean puppets?
I'd say that this is probably the normal silliness, but I have read several articles that seem to indicate S.Korean intelligence has more reason to believe than usual that the North Korean government is in trouble. No telling what the Norks will do if they really feel their slave state might implode.