Has anyone ever shot down a helicopter with a handgun? You see it on TV and in movies, but it seems like a hell of a long shot!
It's conceivable. However the reason the minigun was invented was to shoot down helicopters. The thing is, shooting down a helicopter is in one sense easy, because the rotor is weak and if it's shot, even by a small bullet, the helicopter is done for. So you don't need a cannon.
However the rotor spins rather quickly. So it's pretty much impossible to aim at. So you don't have a lot of odds of hitting it with just one bullet. Enter the minigun, which is called "mini" because it fires rifle-sized ammo, but fires it at an incredibly fast rate so the odds are that one of the torrent of bullets coming out of the thing will hit the rotor.
Still if you did hit the rotor with that one bullet, the helicopter's toast.
You have a much better chance of aiming at the helicopter pilot, though, which is probably what the guy on the ground was doing.