Everyone makes it sound like this art project was tried with a real autonomous car, but it hasn't been.

This is just a guy sprinkling salt around his regular car.

So that was just him driving in and not an autonomous car? https://vimeo.com/208642358

The car drives into the salt circle then stops.

Yes. From the interview above:

Is this actually an autonomous car, or is it conceptual?

I don't actually have a self-driving car, unfortunately....

We're talking about it on HN, so I'd say he did it exactly right :)