Taking a minor look into history and we can easily find what happens with larger stockpiles of weapons if they don't get destroyed after wars (or cold wars). They get stolen or sold. They get used for new purposes which originally they never was intended for.
I find it a fair case to argue that countries who do not destroy their large stockpiles once the war end are to a degree responsible when the weapons are reused in later conflicts outside their border by people we would classify as bad actors.
No, that's the entire point of my example. The military's primary job is to defend us. It's a major failure when their weapons are used against US citizens.
If you accept the premise of the article, that these were "broken arrow" military weapons, sure, I see how you can get yourself into a tizzy over it. But you should not accept the article's premise, because that premise seems self-evidently broken.