Other mistake: After Bruno and Lutz had been arrested and are outside the police station arguing, in the background in the left corner, there is a gold Ford Mustang. Then as Lutz is walking away, the same gold Ford Mustang is seen driving in to park in that same place.
Other mistake: Throughout the movie, the subtitles for Bruno and Lutz translate everything from German to English. When Lutz carries Bruno on his back from the restaurant, he says "Herr Bruno", and the subtitle should say "Mr.Bruno" but says "Herr Bruno" still.
Answer: This is not a hidden camera movie. Everyone filmed believes they are being filmed for a documentary. So the swingers knew they were going to be filmed, but didn't know the shenanigans SBC was going to pull. The camper dude probably started realizing there was something weird going on and got mad that he was being made fun of, so knocked over the camera.