One of the tests is for backing the vehicle up. In that test, you may not touch the curb. It's not otherwise obvious from the document provided that any other contact with the curb is disallowed. So either it's untrue that it's disallowed when pulling forward, or it's untrue that you know about it upfront.
Regardless, not touching the curb, even if arbitrary, can be an indicator of competence. It demonstrates control and awareness of the vehicle.
Memorizing an algorithm is a potential indicator of many things, not all positive, but I don't think it says anything at all about competence.
> ...you can't inch forward until your front wheels come to rest on the curb. ...if you still contact the curb, then you've demonstrated that you don't know where the boundaries of your vehicle are.
This demonstrates one reason why whiteboard interviews aren't great. They don't mean what people think they mean, and people think of them in very black-and-white terms. X always implies Y, or at best they say, "Well, maybe not, but..." and then justify the exact same result with only superficially different reasoning.
In your example, the driver might have demonstrated he doesn't know where the front or rear of the wheel is exactly. But it could also be he was just nervous or driving a vehicle he isn't used to using. Maybe he had to borrow his older brother's car when mom's broke down at the last minute. Saying he doesn't know where the boundaries of his vehicle are goes against all the other evidence: he didn't strike anything with the boundaries of his car. The curb is already inside those boundaries, intentionally and by design of the test.