I think its the other way around. Python became the language of choice for AI because it was already popular. Lots of things made it popular: use for systems management scripts, web apps (Django, especially), then numerical stuff,...
I think the reason is that it is easy to learn enough to get things done, but it is very flexible, very readable, and once the ecosystem started gaining momentum (which it clearly had by the time of the XKCD cartoon) that became an advantage too.
Python's success is explained by it being the language of choice for AI.