I believe the word you mean is improbable. Nothing is impossible. And you may be using the later versions of the test. I'm not saying he was the smartest in the world, in fact, it may have been a flaw of the test. It was when the tests were being first developed. Regardless of what his intelligence was (it's far lower now thanks to a stroke he had a few years back) I'm just saying that it doesn't mean as much as it did.