It's closer to "ice cream sales cause drownings".

A government becoming more totalitarian WILL reduce crime, to a certain breaking point. Part of that totalitarianism could be gun grabbing. As pointed out in a post above, the timeline they quote ALSO had massive draconian (and nowadays labelled "racist") crime reforms that were likely the real primary contributor to the criminality stat: Both "variables" were results from a third related variable.

Much like high temperature causes both more people swimming and thus drowning, as well as ice cream sales, they can be correlated, they ARE correlated, but they're both caused by a third agent. Buying ice cream won't result in someone drowning, and drowning someone won't result in Haagan Dasz's stock price going up. Draconian governments feel no guilt at stopping random people in the street and strip-searching them for drugs or weapons, reducing crimes related to these things. Likewise, draconian governments grab guns.

It's a minor but important distinction from your example, where the variables aren't actually really correlated at all.