It seems to me that it would be valid for the law to consider anyone who is at the controls of a vehicle, while the vehicle's engine is running, to be “driving” that vehicle, even if the vehicle has not actually in motion. Surely, you are considered to be driving, if you are stopped at a stop light.
On the other hand, it could be a valid defense that the engine is running only because the occupant wants heat or A/C, and the occupant could claim to have had no intention of actually causing the vehicle to move.