Most people are intelligent, that's why they can get good, but being smart not only has a big effect on the ceiling, but also on the speed to get to the same level, which in turn affects motivation, so you can't judge it to be an inferior factor
But this isn't a good illustration anyway since it's a very constrained artificial example of a game based on pattern matching
I see examples of that pretty much everywhere. People that regularly do and practice something get to be better than the vast majority of people, so talent and intelligence end up playing a lesser role. This is true for physical skills and also mental. The author said he ended up in the 95th percentile -- I doubt this is achievable for all people, but "high" yes (whatever the interpretation of high is).
But this isn't a good illustration anyway since it's a very constrained artificial example of a game based on pattern matching