The law is pretty clear cut. You have to be operating a vehicle under the influence. If he got a DUI for having a beer on a workbench he can easily argue that he wasn't driving and it would get thrown out. That sounds like absolute bullshit and I won't believe it unless its backed up with court documents saying they actually arrested, charged, and fined/imprisoned him for a DUI while washing his car with a beer open on a work bench. There have been plenty of times where i slept in my car to sleep off the alcohol and have been woken up by cops and NOT been charged with a DUI. Why? Because it isn't illegal.
It's not clear cut and you got lucky then or didn't appear intoxicated, in many if not most places it's a crime to sleep in your car as well. You probably just met with an understanding set of officers, again you were lucky.
Many have been arrested even sleeping in the backseat. The problem is the law usually has an intent to drive clause in it that is pretty well open to interpretation.
Good luck taking it to court too, as in almost all states you cannot drive at all until you win the case. I'd just do some nice easy google searches. All the proof you can want is out there. I got to see it first hand. In my class of about 50ish people, not one had any incident with another vehicle or person other than having a drink that night IIRC, if there was anyone it was probably the only one.
Search for Montalvo New Jersey dui, this made pretty big news about a guy sleeping it off. Even though the NJ laws are pretty 'clear' on operating a vehicle is a requirement, this guy still got nailed. That is just one. There are many.
Also in many states you don't get a jury trial, you can't plea bargain...the judge has to give the minimum sentence at the very least, they are not allowed discretion. Also in most states you are looking at two trials, one is the 'traffic' one which is not bound by most court rules and then the 'criminal' trial.