The comparison between machine and humans uses the results of the average human driver. Not all humans are alike. Some cause accidents, others don't. There's some randomness involved (every human might be the cause of an accident at some point), but most accidents are caused by individual behavior of specific humans.

For a convincing comparison, remove all those human accidents caused by intentional violations / reclessness, looking at their phones, and known but ignored medical conditions. And compare again.

On average we might be safer with all-AV traffic. But we might be even safer by removing the most dangerous drivers and allowing the rest to continue to drive manually. That's the capability of automation to aim for, not the average human.