With physical abilities this is more accepted but I don’t see a reason why mental capabilities would be any different. Some people just have more powerful brains by birth. You can achieve a lot by exercise and discipline but some people can achieve higher levels than others.
Then he also studied math and then won the Putnum. How would he have gone without doing all that "non-study" about problem solving and looking at problems from different ways and just doing math quite well? Maybe he was so brilliant he still would have won? I suspect not. How many others sitting for the Putnum had done similar amounts of the same quality work by way of preparation?
Genius? Or learned and honed? Both? In what proportions? Whatever I think about it is "Just like my opinion, man." Right?
Yes, you tend to get good at what gives you a buzz, in a compounding way. But I expect 'buzz' isn't random, either: it'd make sense for personality formation to notice when you show talent at something valued by some of the people around you, and flip some motivational switches in your developing mind. This seems like a better bet for your genes than trying to engineer your motivation and talent towards a common target separately.
You can't just train to win the Putnam if you don't have the talents. Have you ever sat and worked problems with someone exceptional in that area? Try it if you get the chance. The variation in ability will blow you away.