It's kind of like how I say it's " my " phone, " my " room, etc. It's only mine because my parents are letting me use them. I don't need them, I won't die without them.
And if it was his property he could have called the cops or something for theft, but for the most part he probably didn't buy that car himself, especially if he's bad enough to still take the car out when he's clearly not allowed to drive it.
If I remember correctly, in our country, if you have a safe used to store valuables or guns, it has to be bolted (at least) to one floor surface AND one or two wall surfaces, according to law and insurance policies. Ideally, it also has to be hidden from plain sight. We've had a lot of crime where people just break in and steal the whole safe.
And if it was his property he could have called the cops or something for theft, but for the most part he probably didn't buy that car himself, especially if he's bad enough to still take the car out when he's clearly not allowed to drive it.