Tone of voice is just as important. I have an in-law who’s a cop, and most times if you're a jerk, he says you get the ticket you might otherwise not have. It’s very much an issue of power because someone needs to control the situation—you or them. Not to mention, being argumentative gives them a reason to suspect something else might be going on, and in turn, mess with you. Why give them that chance?
I wonder if he would try another experiment where he actually answers the questions as asked, but instead makes his tone sarcastic, etc. I bet he's pulled out of line just as quickly for cooling down, even though legally he’d have complied.