Just because crime goes down as gun ownership goes up does not mean that more guns = less crime. Crime can be so many other factor, too. In fact we could say, as we economists are prone to do, that "all other things being equal" gun ownership may increase crime even though this data set shows gun ownership increasing and crime decreasing. The problem is that not everything is being held equal. The crime could have decreased due to a number of factors not related to guns. Things such as other policies (jail time, punishment, law enforcement funding, etc etc), demographics (people moving out of inner cities into less dense suburbs, etc), and the economy (granted we normally see a negative relationship between the economy and crime, but that's just an example).
Do not fall into the "this because of that" fallacy. That is too easily defeated. What we should take from this is that crime didn't go UP like many said it would. Or if we can isolate some of the data we can draw conclusions from that. Things like gun crimes didn't go up. Or states with more free gun ownership saw a larger fall in the crime rates (if that happened). The FBI crime data is beautifully in-depth and there will be a lot to be drawn from it.