Remember, A-Train is a Bill only because he's a crony...
Willis may not win any IQ tests against bricks any time soon, but 3rd or 4th he knew the job was to get a first down on the next play and, for whatever reasons you want to attribute it to, he didn't make it. DO you think his effort/mindset would have been different enough to make a difference if he thought it was 4th, even though it's clear he's stupid enough not only to not know what down it was, but also to admit it to the press?