The NCIS numbers do not include gun show sales and exclude previously owned guns. It only reflects new purchases.
In the case of Texas some of the private firearms have been in the family for 2-3 generations.
So these numbers do not mean much.
It's not just Texas my FRiend. Collectively, as an extended family, I have access to an impressive arsenal, most of which are pretty old guns, some dating back to the 1800s. Most are in firing condition when you can find ammo for them.