Actually, I don't think it means that at all. I came across a definition of "well regulated" that I now keep on my FR home page, which, knowing how 17th and 18th Century armies operated, makes the most sense of any explanation I've ever seen:
The term "regulated" applied to clocks means "accurate in keeping time". It made sense, particularly in 18th Century armies, to have to pay a lot of attention to how well soldiers could operate in massed formations. Soldiers had to be drilled to load, aim, and fire as one unit. You do NOT want the rifle next to you to be firing (and emitting a shower of sparks) while you are pouring gunpowder into your musket. Everybody had to do every step together with no screwups.
One of the main reasons we revere General Friedrich Wilhelm von Steuben is for his abilities in training Washington's raw recruits to do exactly that. From von Steuben's wiki page:
But battle was close-order drill, and speed of firing could only be obtained by drilling men in the handling of their firearms until the motions of loading and firing were mechanical. Firing was done in eight counts and twelve motions:
Again, these cartidges were blackpowder wrapped in paper, and the pan was primed with loose powder, often obtaining by tearing the paper with your teeth and pouring a little into the pan. You did not want the guy next to you, or in the rank behind you, firing, while you were in the middle of handling that cartridge.
You are correct. That is exactly what “well regulated” means.