If the "extremely precise requirements" can be cheaply and automatically validated, it's much easier to have the AI generate spam on a loop until it passes all the tests.
They’re not really making any claims about how quickly the AI can solve relative to the validation, which is what P vs NP is about.
Yes, Cline generates a bunch of junk very quickly and makes dumb mistakes. If I can filter out those dumb mistakes automatically, I don't have to supervise it. It might burn 20¢ on fixing a mistake no human developer would make, but I don't have to pay a human developer.