The leaked email has his name on it and the leak claims it was an email from Elon to employees. Can't really tell if the leak is real or fake, but if it's real then Elon is definitely the one who wrote it.
Based on his proclivity to say dumb shit and his inability to keep his mouth shut, I'm inclined to believe it's a real leak.
Or he's just a narcissist that can't run a company if he's not held on a leash by people who actually know what they're doing.