Here's the basic backstory: Guy orders Model S from Tesla demonstrator stock (what the company calls "inventory cars" and sells at a slight discount), guy waits for Model S, guy never gets Model S, guy is repeatedly ignored by Tesla staff. Until he finally gets through to someone and they tell him the embarrassing truth. The car he had picked out was actually earmarked for internal use before it got sold. And Elon Musk himself was using it to test out the latest iteration of autopilot. He thinks Tesla avoided his calls because they didn't know how to break the news.
So Musk didn't really steal anything, at least not on purpose. It was a simple clerical mistake, human error. When you think about it, it is kind of surprising coming from a company filled with computers and technology that's trying to change the way people buy and use cars. The post's author, Marty, eventually got his $4,000 deposit refunded. We're guessing he won't be a repeat attempted customer.