Your overall point is well taken, but you're interpreting "century" to mean "last hundred years". The way I'd interpret the word, this is a candidate for understatement of the last century. And the winner was probably somewhere near the Trinity test...
"Now I am become Death, the destroyer of worlds." Strikes me as just statement statement not over or under (I'm assuming this is your reference?)
From the final chapter of his new book Cowards, titled "Adapt or Die: The Coming Intelligence Explosion."
The citations for the chapter include: