Musk is probably really good at back of the envelope calculations. The kind that lets you excel in first year physics. That skill puts you above a lot of people in finance and engineering when it comes to quickly assessing an idea. It is also a gimmick, but I respect it. My wild guess is that he uses that one skill to find out who to believe among the people he hires.

The rest of the genius persona is growing up with enough ego that he could become a good salesman, and also badly managed autism and also a badly managed drug habit.

Seeing him dabble in politics and social media shows instantly how little he understands the limits of his knowledge. A scholar he is not.