People are people, and people do weird things...
There's a lot to consider... is your gym particularly known for producing top gymnastis in your area? If so, that's one thing...
Two, lots of coaches like to see how judges are juding so they can compare to how they judge their own athletes...
Three, some coaches are just unaware of the rules (or, never read them other than glancing at the pictures in the routine book), and get frustrated when other people score high for "the same routine as their girls" and do strange things out of frustration.
Four, some people simply enjoy the sport.. did they record ALL the gyms or just yours? Again, if just yours refer to question #1.
Five, some people are just weird and have their reasons. However, unless the venue has a non-film/camera clause in their entry requirements (which is close to impossible, really), competitions are a public area where people may basically do whatever they want within legal limits - and using a still or video camera is completely legal.
It's a sore spot for many parents. If it bothers you, feel free to ask the individual kindly (read: non-accusatory) why they are filming/shooting, and express that you would rather they skip over your child (or child's gym) because it makes you uncomfortable. Some people may accept your request, others will become defensive and cause a scene, yelling at you for trying to censor them.
People are people, and people do weird things.