The 'guns per capita' stat (or slt, maybe for adults, dunno) has increased from approx. 5 up to approx. 6.5 - a ~33% increase, which means you aren't getting new gun owners at a rate to keep up gun ownership rates, that is what has fallen.
A wholly-artificial stat, since the only basis the FBI has for concocting it is documented transactions by individuals going through their official background check. If that were the only legal way to get a firearm and everyone lived singly with no households, then it might have some validity. It's a bullshit number, nobody actually knows what the real figure is or what the delta, if any, might be.