I don't follow the civil war bullshit, but to be fair, the FBI puts the estimates of total privately owned guns at close to 300 million, and gallup says around half of American households have a gun. Guns are hardly the realm of a tiny minority.
I'd also note that supply is currently woefully short of demand. Distributers have nothing to distribute, the market for anything that might be banned is all but completely dry and/or gouged to all hell. That means there are potential buyers out there who will not get a gun. Those NICS numbers you cited only indicate the number of guns sold, not the number of people trying to buy guns, which is likely much larger.
Also, a gun is not a disposable good. In many cases people buy guns and keep them for a lifetime. So while the number buying new guns may be relatively small, there may be millions who are simply happy with their current AR-15/AK/whatever and stocked up on magazines or other goods, or just didn't buy jack squat.
My point being, those NICS numbers don't effectively quantify the number of assault weapons enthusiasts, who by the way are not all paranoid survivalist morons.