A reader of The Tuesday offers:

At the risk of piling on to what other math pedants are telling you, I think it unlikely that Musk would use “500 percent less” to mean 1/500. First, “500 percent more likely” means 6 times as likely, not 500 times: 100 percent more means twice as likely, 200 percent more means three times as likely, etc. I would guess that Musk (quite mistakenly) takes “500 percent less” to mean the inverse of “500 percent more”, although I suspect that he adds error to error by thinking this means “1/5 as likely” rather than 1/6 as likely. “500 times less likely” literally implies a negative likelihood, minus four times the positive likelihood of the status quo.