I don't think he's a moron - you don't make a fortune with Paypal, then with Tesla, and build a commercially successful space launch company with advanced engines, reusable rockets, and an internet satellite constellation, if you're a moron...
He's very clever in certain technical areas, but not as clever as he thinks he is in other areas. Self-destructive? Maybe - but then he's splashing around in the world's biggest bathtub full of cash and he doesn't seem particularly bothered if he loses some of it over the sides.
Not in the old "IQ scale" form, but rather moron as in fool, or knave.
Clearly Musk is of above average intelligence, but as far as Musk's technical prowess, I'm not sure what that would be.
He nearly, but did not, finish a BS in physics.
Then he wound up in some digital payments start-up in which he must have had some sort of stake (X.com; not sure what he did), that got bought out by a similar company across the hall (PayPal). Eventually Musk ends up as CEO and gets a ~$1/3 B payout when PayPal is bought by Yahoo!
He did invest wisely his wind fall in two new companies that were poised to break big -- Tesla (electric cars) and SpaceX (private rocket ships)
With Tesla he did not found the company (though his fan club would like to think he did) or invent the electric car, but bought into a fairly small version of the company, forced out the founders, and drove expansion. He clearly did this very well and got very wealthy in the process. (It did not hurt his wealth and perception that so many people treated Tesla like a tech-startup rather then a manufacturing concern.)
He was actually in the start of SpaceX. He found the people he wanted to fund and latched into the new commercialization of space effort.
In both of these successful cases, he is able to better understand (but not necessarily design) the technology than many CEOs and major investors in new technology and it certainly has helped his wealth. (For a counter example, recall that after Jobs left Apple the board hired the CEO of PepsiCo. That did not work out well for them.)
Of course not all of his ventures are successful and HyperLoop might be one of the dumbest ideas I've ever heard.
TL;DR summary.
Musk is not a "Stanford-Binet" moron, just the "frat boy ingesting 151 rectally" kind.