"By default, driverless passenger vehicles and trucks can ride anywhere in the United States, unless a state explicitly says they can’t. " how is that possible

"By default, driverless passenger vehicles and trucks can ride anywhere in the United States, unless a state explicitly says they can’t. " how is that possible? what constitutes a "driverless" vehicle? If I build some piece of crap in my garage that barrels down the road and nearly kills ten people, versus one of Musk's cars does the same thing because of a bug in their touchscreen, these are both "shrugs, what can you do?" situations? I'm pretty sure I'd be arrested and Musk would not.