I don't think it was applied in the other direction though I do see the problem with TSA's article, it seems to debunk itself by considering absence of evidence to be evidence of absence. It only allows that in one way however, not the other.
But there has to be a claim, and the claim is that the gun ban was effective, and the evidence cited was the lack of the very rare mass shooting. So a more accurate claim would be "thus far it appears that..." . It would be more accurate than drawing any other conclusion for or against, but since the act of making guns illegal was an extreme measure, you really need more than "jury is still out" to support it when you try to use Australia as an example.