This really does seem like the (almost) best-case outcome for this scenario. The driver should never have been behind the wheel, but if it had been almost any other car, he definitely would have crashed, and a crash at highway speed would almost certainly have injured him and could have injured or killed others.
It sounds like the driver may have been slumped over the wheel, which could have created enough steering resistance to make the car think his hands were on the wheel. Teslas don't currently have any other way of detecting driver attention.
GM's SuperCruise uses eye tracking to monitor driver attention, but it's apparently really finicky. I'm not sure if there's a better solution right now.