Given that some people go around calling themselves Happiness Engineer or Growth Engineer I highly doubt that people in SV care enough about the difference. Also you can major in Financial Engineering at Princeton so I don't really think people take the FE exam before calling themselves 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.