Isn't that the point of the statement though? You do it for yourself, not because anyone else at all might want to use it. Then if you toss it up on the app store and anyone does actually use it, it's just a happy upside.
It would make more sense if the example were of an app no one ever knew about, if that really was the case. His app provided more of a counterexample, if what you're saying is true.
I took the fact that his app became popular as a happy accident. That he made it mostly to satisfy himself, because he was, in his words, "scratching his own itch". That it worked out on the app store was just a nice benefit, but not really part of the motivation. Or such was my interpretation, maybe I have it wrong.