When it comes to research papers and numbers and percentages, things can get kind of interesting. Of course data can always be manipulated.
Along the same lines, here's some stats that include world wide civilian, military and police firearms. Some of those numbers seem awfully low as well.
Since the over 18 population of the US (2010 Census) is 194.3 Million that would be appx 5% who admit to carrying. Noting many states don't have CHL and no way to track how many carrying. Not bad numbers at all.
Statistics! Looking at the journals own article it says "researchers estimate". The bullet below is interesting since it implies people carry but neither concealed or open so what is the other choice?
Think about being surveyed. If someone blindly asked if I carried I would deny so an under reported count and I suspect a certain population would do the same. I would also assume the guy who illegally carries and holds his Highpoint sideways isn't too forthcoming either.
Of those who carried loaded handguns, about two-thirds reported always carrying them concealed while 1 in 10 reported always carrying them openly.