Everyone I know who only owns one gun doesn't know squat about guns.
My old man only has one handgun (and one hunting rifle), and still manages to out shoot me on a disturbingly regular basis.
The only special forces member I know on a personal basis only has one gun.
When I was in college I only had the one - in large part because I spent all my gun budget on ammo rather than other guns.
While it's true that many shooting enthusiasts wind up becoming gun collectors, I don't see one as having a whole lot to do with the other.