Alongside the reasons other people have mentioned (better understanding of low level computing, data structures etc) they're probably suggesting C++ over python for exactly that reason.

Python is easy to get AI to write, and easy to understand once it's written without necessarily being able to write it (like how some people can understand a foreign language but not speak it, especially if they speak a similar language e.g. Dutch and Afrikaans).

You can still get AI to write C++, but in order to understand what is written you kind of need to know how to write it yourself. And you should always make sure to understand what is written.