Isn't a "fleet-wide hack of autonomous vehicles" an oxymoron? They clearly aren't autonomous if they are controlled by an outside force that can be hacked.
Maybe it depends on perspective, with the manufacturer seeing owners as outside forces, from which their vehicles are autonomous? Rolled up with the liability question is the question of who does control the vehicles and who they are autonomous from.
The vehicles are autonomous when asked, such as if you click "summon" in the app. If they gained access to Mothership after summon was introduced (they accessed it in 2017, but summon came out in 2019[0]), it could have meant accessing a car and summoning it to attacker.
"Autonomous" in this instance means "able to maneuver without a driver", not "able to make independent decisions without the help of an external system".
Maybe it depends on perspective, with the manufacturer seeing owners as outside forces, from which their vehicles are autonomous? Rolled up with the liability question is the question of who does control the vehicles and who they are autonomous from.