I'd guess someone charging a single phone would not be arrested, but how about someone charging 100 phones, or 600 phones?
Charging the car for 20 minutes uses about as much electricity as fully charging from empty 100 iPhones. It uses it at a rate equivalent to trying to charge something like 500 iPhones simultaneously.
If you're going to add any value to these numbers, don't leave out the estimated damages. In USD that number apparantly is 0.05.
I understand that they don't want to risk a very high electricity bill, but if the damages are about a nickel, then keeping the man in jail for 15 hours is extremely and inexcusably excessive, in my opinion. I understand that they want to send a signal not to randomly plug your electric vehicle in sockets, I sympathize with that, too, but not the resulting action taken by the police. Not over a nickel.
Cheaper to put a sign or lock on every outlet, than invoke the legal system once? I'm not sure about that (especially if this doesn't go to trial. It may still be preferable, but I'm skeptical about cheaper.
I doubt this is going to the only case. Electric cars are going to become more and more common, and the hunt for an outlet at a parking lot is going to start mirroring how it looks at airports with smartphones.
That said, I bet there's more to the case in the OP than we're seeing. Probably they've told this man to stop before and he keeps doing it.
They don't arrest you for plugging in your smartphone in an airport. This is precisely an attempt to prevent it from becoming common. If everyone knows that is not something you do, then you don't need to put up signs.
Charging the car for 20 minutes uses about as much electricity as fully charging from empty 100 iPhones. It uses it at a rate equivalent to trying to charge something like 500 iPhones simultaneously.