It is not easy to grow up being labeled as a genius. One day you realize that most of the people of your age are so far, far below your ability it's just sad. You try to help them, but everyone know it's not easy at all. All the work you've done to get to this level seems to be very natural for you after all these years, and you have no idea that most of the kids were not doing _anything_ in their childhoods. Then you got this feeling that all your "genius" skills came undeservedly and it's really depressing, because they constitute your person, and you really would like to believe that you got there by your own work, cause it does not feel fair otherwise.

To work out this cognitive dissonance, you start to look what you did differently than your peers and you notice that you were doing math (or cs, or electronics, or biology or whatever) as early as you remember, while your averagely performing mates from university only started doing something serious in university classes or maybe in high school. This feels like a pretty good explanation, especially when one takes into account a 10 000 hours rule, but being a rationalist (who you surely are), you cannot discard the impact of your genes, but as long as it is not measurable, you can believe it's small.

That's how you come to the state of mind when saying things similar to the quoted ones seems pretty natural and not at all out of touch with reality.

(I say this from my own experience, so it's easy for me to sympathize -- I'm not as brilliant as the guy from the article, but I'm getting two bachelors (math and cs) next year, by then being 20.)