It certainly doesn't sound like Twain. That first sentence is awful.

As far as Rumsfeld, known unknowns means knowing what you don't know the answer to, his problem was more with "there are known knowns; there are things we know we know.", because obviously he needed another category there as well, the incorrect known knowns.

Exactly: he listed known knowns, known unknowns, and unknown unknowns, but completely neglected the one that got him, even after the fact.