I was poking around near the river, heard gunfire, and went up the hill and discovered that one of my settlements was under attack - I don't remember the name but it's the one where they give you the mission to kill the feral ghouls at the National Guard facility.

There are only two people there, and they were being attacked by four Super Mutants - at least one of them, according to VATS, was low on HP, and at one point, though I can't be sure if this, it appeared that one of them had been knocked on the ground and was shooting from a seated posture.

I managed to draw the Mutants away and defeated them myself, but I doubt I would have survived if I had the same gear as what the settlers were using. Is the "shooting while knocked on the ground" something that happens in place of actually dying for settlers?