I don't think there is a good lesson about C++ directly. As far as I know, the way the contest was designed success would be pretty much programming language independent. I.e. you could easily port the code from C++ to Python and the result would be the exact same (aside from the 1 second limit per move).

If I had to guess, I'd say that this is because AI experts use C++ a lot. AI can be very computationally intensive and having close control over memory can be useful. I remember a prof who did NLP saying this exact thing.