I know exactly what happened. Polarity was reversed, and something got destroyed. This is often protected against on the big electronics, but sometimes there are parasitic current paths go ground that can easily damage an ECU or something like that. Reverse polarity is never a good thing. It's possible that one of the sensors that gets direct battery voltage could have got damaged also, tough to tell because every car model has different electronics and those electronics are protected differently and susceptible to damage in different ways.

Once the code is read you'll be able to tell more. Luckily everything is easily replaceable if it's been destroyed. This stuff gives me nightmares though, you can be as careful as you want with your own car and then someone can randomly fuck it up for you (whoever jumped it in this case).