Interesting, yet you're talking about a specialist subject.
In my own experience affinity definitely plays a role. Some areas easily clicked with me in school while trying to help very motivated others didn't get them to the same level, In other areas it was the other way around. It's of course easier to get motivated for things that come more easily to you.
The question is can they repeat the experiment with other kids, or is it an exception. Siblings aren't perfectly similar in ability, yet they still share many of the same genes. And chess is also a very specialist area. It would have been interesting to see if her IQ changed dramatically over time. You can raise your IQ a bit over time with practice, yet can you go from 100 to 170 by working hard?







