Riot shot shells are a small pellets(#9 or smaller) and use a type of wadding that quickly spreads the shot as soon as it leaves the barrel. Riot guns usually have no choke or tightening of the barrel near the muzzle(which helps to concentrate the shot into a tighter circle). The power of a riot shell can vary, depending on the shell. The idea is to get as wide a pattern of pellets as possible as soon as the charge leaves the barrel. Close range, it is as deadly as any other gun.
This is quite different than a quail hunting shell and gun. Those that were probably used had 7 1/2 or 8 shot and a slight choke(improved cylinder?) as well as more power in the shell. Also, the wadding used is made to keep a much tighter pattern of shot out to 40 yards or so. This setup will produce a pattern of shot that will be bad news to anyone close by. I know from personal experience that at 80 yards, #6 shot from a hi-brass(power) shell and a gun with a modified choke(pheasant or rabbit load) will penetrate a canvas hunting coat.