He is comparing situations where human decision makers are highly trained professionals such as astronauts and passenger plane pilot to daily driving situations where the average human decision maker is more likely to be an idiot(people switch off while driving) distracted by his smartphone.
Even a "switched off" human is benefiting from the supervision of a brain that is far more complex than any computer yet constructed, and has, on average, been trained in driving by decades of experience, and in recognizing patterns of movement by millions of years of evolution. Meanwhile, computers in cars today cannot even reliably translate human throttle inputs into throttle actuations (see: Toyota).
Let's be fair. Not much of our millions of years of evolution has fully prepared us to tackle the slew of random events and conditions the daily driver has to face. And while our hundreds of thousands of years of tool use has certainly managed to have some influence on our genome we're still barely equipped to operate tools that increase our speed, strength, and carrying capacity by orders of magnitude. This is demonstrated every day by the astonishingly huge number of terrible accidents caused by these tools. Automobiles are responsible for perhaps the most (no doubt due to the vastly varying levels of skill and practice across their operators). Human decision making is simply not fast enough to handle all of the situations one can encounter while operating a motor vehicle and is certainly many times slower in any given situation than a highly optimized specialized system designed to solve that type of problem. The area where human brains currently have the advantage is in reacting to novel edge cases, but at that point providing adequate autonomous conveyance at safer-than-human accident rates becomes a numbers game.