Here an example. I’m on the freeway in my Tesla and instead of staying behind a car, at a safe following distance as predicted, I change lanes and speed past. Was it because, 1) the car was doing something I perceived as dangerous and I moved to a safer position, 2) I’m in a freaking Tesla and I can

Tesla's shadow mode is collecting real data up until the point where the car's decisionmaking process and the human driver disagree. Everything after that is simulated fantasy. And since human drivers aren't necessarily going to do "the right thing" in all circumstances (there isn't necessarily a single 'right thing') you can't treat 'car-disagrees-with-human' as an error case.

Other cars respond to your actions, so the moment your actions deviate from the bot the reactions of the other cars are no longer valid to test against.

Backtesting a driving model, it’s very hard to tell what would have happened, had the car deviated at all from what the driver did.

e.g. You see the driver swerve for no apparent reason, did the driver simply drive more recklessly than the car would, or did they avoid an obstacle the model didn’t catch?