Rush said: "While there's obviously risk it's way safer than flying in a helicopter or even scuba diving. There hasn't been even an injury in 35 years in a non-military subs."
He also apparently said something like "almost all sub accidents are the result of pilot error".
These are both because almost all subs are certified for safety. A certification he specifically chose not to get, because of his belief about pilot error. The risk of mechanical faults is all but eliminated, leaving pilot error as the only likely risk - without the certification, mechanical faults are much more likely and, in this case in particular, almost inevitable.