
Mark Twain was a writer in the late 1800s in America who wrote some real novels, but also is mainly known for his humorous and satirical writing. He’s exaggerating here for comedic effect, not trying to be serious. So it’s probably a combination of the older language and the fact that he’s trying to be funny.
It would suck for the Atlantic and Jeff Goldberg, but I almost hope that they charge him with distributing classified info for posting the plans. The courts would absolutely WRECK the government in that case