The exterior and interior of the door handle are the same wire as far as electricity is concerned - there is no resistance between them. It's not like it's going to magically unlock but the motor will be toast.
Yes, in theory because the two surfaces are connected they are one wire, but in practice metal does not have a non-zero resistance until you get down to absolute zero temperatures.
This subtlety is what allows one to do something neat like this: https://www.youtube.com/watch?v=fPoomwdNZeY - on their build log you can see the musician does accidentally hurt himself from time to time when bits of his chain-mail don't make for complete coverage but he never goes into cardiac arrest. The current allows goes for the shortest, least resistant path to ground.
A similar effect is also what determines survival rates in lighting strikes. If the current passes through the brain it can arrest breathing, or through the heart and it can cause arrhythmia. If it just passes through a smaller area like a finger it can do more local damage but you'll survive. This is despite your body being 70% water or the equivalent of 'the same wire.'
If you wanted to "shock" Lockitron's motor you would need to ensure the motor is in the current path - this is pretty difficult as it's isolated in a plastic container with only two wires grounded it with the pcb, itself mounted in plastic.
And how exactly do you attach one of the car battery cables to the inside handle if the door is locked? The point is that touching both cables to the front will result in the shortest path between the cables, which goes through nothing useful.
