I'll chime in to the discussion of law among non-lawyers. Kinda like arguing in a bar.

In the case of the shopping carts, I still doubt that that is an automatic slam dunk, but suppose it is.

The shopping carts are the property of the store/mall. Presumably the keys the idiot used on the Crossfire are not. I wouldn't imagine the mall is responsible for what someone else does with their own keys. Beginning and end of comparison.