The cop got an answer he didn't LIKE, so he harassed the kid. The question was answered - in a full sentence, according to the transcript. But it wasn't the answer the officer WANTED, so he escalated the situation.
Well he didn't want to get interviewed so the cop forced an interview. </sarcarsm> What the cop meant was that Brett didn't want to get interrogated, so the cop decided to force a roadside interrogation. But dang it, he forgot his standard issue rubber hose and bright light.
No one likes smart assed answers from a brat kid.
That aside, belligerence is a sign of drinking and drug use. The cop didn't handle it right, but it is the right thing for a cop to follow up when someone shows such signs and they are behind the wheel of a car.
The question was answered
In a belligerent manner, as I've already pointed out.