Why did this man pull a gun on someone else in a snack bar?

This footage, dated to August 19, 2017, shows a man (in a white tee) in line with his family at a snack bar in Brazil. There's another man (in a blue hooded sweatshirt) next in line. The family appears to be ordering their food. The man waiting in line behind them is tinkering around on his phone, as one does. All of a sudden, the man in the white tee whips out a gun and threatens the man in the blue sweatshirt.

The footage is low-res and there's no sound. What was the man in the white shirt afraid of? Perhaps they know each other and are sworn enemies?

Well, you'd never guess, but it turns out that it's a cop who thought the guy in the hooded sweatshirt looked suspicious.

At least we can take comfort in the fact this sort of thing doesn't happen in America!