You really think he wrote it? He has an army of engineers working for him, many of which would kill their mothers to get on Elon's good side, corporate culture is same shit different smell no matter the corporation.
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.