Frankly, that's also the most plausible situation independent of what we've learned anyway - it would be fantastically hard to advance technology by ten years entirely in secret. They wouldn't have the benefit of any of the literature released in those 10 years. All their computers and other equipment would be 10 years older, and the sheer number of cryptographers working on these sorts of things at the NSA is almost certainly much smaller than the number working on them outside of these contexts. It would be pretty difficult to pull off, particularly since they can get away with just cheating.