You can't answer unless you know the whole story.
Did the guy throw his hand up earlier, only to speed off almost running over cops? Did he just pull off once cops asked him to get out of car or wait a moment? Was he beligerent? We know he was drinking.
Too many questions to be definitive with an answer. Obviously, the cop had thought about it for some reason because it happened immediately. Doubt it was an impromtu event.
All the articles I've read only list the charges from the chase; haven't seen any DUI charges. Maybe he was, and I'm reading articles with a bias. But how do we know he was drinking?