If you've ever shot a gun or been around guns you'd know the rapport of various guns is not always consistent. Often, it is difficult to tell the difference between a gunshot and a firework for example. Even something like dropping a wood pallet far enough away can sound like the echos of a gunshot. Backfiring from a car can sound remarkably close to a small caliber rifle. If a gunshot doesnt happen quite literally within a few dozen feet of you it's often hard to tell. Typically the way you can tell is people who shoot guns generally don't do it once. Several rapports tend to raise the probability of a gun.

ShotSpotter works in isolation because in isolation a certain noise profile is almost certainly a gun shot. Like most ML aiming to change the world it's powered by p-hacking.