What you are saying would be kind of like someone saying "I knew an athlete who could do a mile in under 4 minutes, but one time he got on a bike, fell and then never cared to try biking again. Therefore, the ability to ride a bike has nothing to do with athleticism." Which is technically true, but misleading. It misses the key idea that the main factor is the person not taking the bike seriously as if he actually decided to take the time to learn how to ride a bike, it's virtually certain he would be better at it than 90% of people because the underlying traits that make one exceptional at running would also make one good at biking.
It also sounds this person had a good temperament and personality which worked in his favor. That wouldn't matter though if he didn't have the cognitive ability to never miss deadlines and correctly design out code in his head and on paper before writing it as you say.