Coming from the civilian LE side, along with some military. The other congregants who rushed towards the suspect after the fact had poor muzzle discipline, period. Yes there is no "safe direction"/"down range" in the real world. There is however a "safest direction possible," and at your fellow parishioners isn't it. If these folks haven't had any training/experience in a large crowd with guns, then mistakes happen (and fortunately everyone kept their fingers off the trigger), but that's what they are, mistakes. If you know that someone isn't a threat, then muzzeling them is a mistake, period. I'm sure the responding armed citizens, didn't think that 78 year old Gladys in the pew between them and the bad guy was an accomplice they simply locked onto the threat, and their muzzle awareness decreased.
At no time working in a military shoot house, a federal LE agency shoot house, or my own local agency shoot house, has it ever been okay to muzzle a known friendly. Doesn't matter if we're doing LE alarm call building search practice, or high-speed-low-drag sniper initiated explosive breaching hostage rescue training, you don't muzzle a known friendly. Unknowns yes, hostiles, absolutely, friendlies, no.
Working in a civilian context, with a large crowds is about as hairy as it can get to have a gun in your hand. Kudos to those who rushed to the sound of the gunfire. Lets just as a community of armed citizens work to be better about the mistakes that were made here, so that the inevitable next time, we aren't making the same ones.