Oh really? Where did he study engineering? When did he take the FE exam?
That's not a term that you can throw around all willy-nilly, especially in the context of hardware. Next, are you about to tell me that the CEO of Ford is also an engineer?
The term "engineer" does not imply chartered/professional status in current popular usage.
Musk, on the other hand, holds a degree in physics. He started a PhD program on applied physics, but quit to pursue his entrepreneurial interests. If you judge engineers purely from an educational perspective, then yes, Musk is not an engineer.
Nonetheless, if we look at wikipedia's description of what "Engineer" means, we get:
> An engineer is a professional practitioner of engineering, concerned with applying scientific knowledge, mathematics, and ingenuity to develop solutions for technical problems.
So, by this definition, Musk is an engineer...
Although I do take issue with the above (happiness & growth) usage of the term, I'm completely fine with Elon calling himself an engineer because he actually did study engineering (albeit informally) via books, etc.