This is always the case. The ISIS videos are online, but I won't link to them (feel free to google Foley beheading fake to see all the screencaps of it, but you have to see the video to notice things like that fact that they greenscreened the whole thing, there's wind in the background and none in the foreground, etc).
Not to be a tinfoil hat character, but this stuff just pisses me off.
I listened to the 911 tapes from the school shooting in the states too - it's a recording of people not freaking out and just calmly talking about kids getting shot and bullet wounds. They also interviewed the janitor and it was his first and only day on the job because the regular janitor wasn't available that day for some unknown reason. Obviously the event took place, but the 911 tapes were as fake as the day is long.
Long story short, everything is bullshit