Stopped by a Bored Cop

An example of how bad the lack of communication is over here, and how people in government positions abuse of their power:

While driving around with my sister, Maribel, we ran into some portion of a main road where the cops set up some cones and were slowing people down. Maribel slowed down as soon as we saw it, but the cop ahead her made a hand gesture to slow down more. Maribel responded and kept slowing down. We were going at less than 5 Kilometers per hour and the cop kept doing the hand gesture as we passed her, and she knocked on the window and said to stop on the side of the road. It turns out that she was somehow trying to tells us to stop and didn't know how to do the right gesture.

On the side of the road, my sister apologized for not getting what the cop meant stop instead of slow down. Then the cop started whining about how she and the other cops set up those cones at 6:00 this morning for our safety and blah blah blah blah. Maribel tried to reason with the bitchy cop, but it was like dealing with an idiot child in uniform. Then she went away and another cop came to take our license and registration. He let us go, immediately

I don't get it. Maribel explains that nobody really knows the true reason why they'd set this up and stop vehicles at random but they're doing it to see if drivers are missing their papers and either ticket them or ask for a bribe (bribes are more common). Of course, cops never explain anything; they just follow orders and have no people skills.