There are indeed statistical issues with the comparison, but I'm not sure it's the one you're pointing out. There's probably enough Tesla miles being driven that we shouldn't worry about the random noise around the mean.

One immediate problem with real world stuff like this is selection. How do we know that Tesla is safer because it is built more safely than normal cars, rather than that perhaps people who are more safety conscious buy a Tesla? After all it's a more expensive car, the kind of thing you might only be able to afford once you're a bit older, the same time that you might have kids to worry about. But older people are also not the type to be racing around fast and furious style. Maybe there's an imbalance in the man/woman distribution?

It's a real can of worms to unpick these kinds of things. You find it all the time in social sciences.

Maybe you can find stats for Teslas without autopilot, or other cars with autopilot, and other cars without auto. And stats for how Tesla drivers are distributed according to age and sex?