Generously, Musk has never been serious about making predictions. When he says stuff like this he just means he's excited about it.
He tends to do it whenever there is bad news in other parts of his business.
That's an overly charitable interpretation of what he's doing.
The pattern that I've observed is: 1) he's a narcissist who always wants to be in the news and/or 2) he's trying to distract from something.
He can't stand it when the press moves on from him. His MO is to wait for a week or two and then throw out something outlandish to suck up the media oxygen.
He and Trump are very similar people.