Extreme DUI for getting a PS3...REALLY?

In Arizona. I was drinking with friends last Saturday and we were going to play some games and my friend forgot his PS3 was in his trunk so he gave me his keys and I went to get it.

I'm standing there with the trump open and getting it when a bright light shines on me and the cops stop me and my friend runs out saying "no it's my car" so they knew I wasn't stealing, but I got a "1382" which is extreme DUI in Arizona. I spent the night in jail and I have a court date.

The car wasn't unlocked, just the trunk, and I don't even know how to drive a stick shift. How can they think I had driven the car there without any proof? Or do I have to prove I never drove the car, ever, let alone drunk?