Those aren't facts. They're opinions, and conjecture based on doctored statistics.
Even the conclusion at the end of your quote bubble states that attributing the decline to the NFA was at best an inference.
In fact, the article itself points to the already declining rate of gun homicides and gun suicides in Australia making interpretation difficult.
As well, your example provides a glaring example of the mis-information the anti-gun lobby spew out, and which anti-gun people buy into uncritically:
The "fact" you suggest is that the ban and buy back reduced
firearms-related homicide and
firearms-related suicides is a disingenuous statistic. It implies the ban and buy back were responsible for the a reduction in homicides and suicides, but it's only looking and gun related.
When then overall homicide and suicide rates (by any means) are viewed, it can clearly be seen that these numbers do not deviate statistically. In fact, one article I found shows that the overall suicide rate actually went up during the buy back period and in 1998
http://www.ic-wish.org/McPhedran Baker Suicide Trends HP.pdf
The fact is this: anti-gun people distort real facts to support an anti-gun fairy tale.
The example I pointed out originally is well understood: that statistic of a 1/2 million gun homicides in the USA spans a huge number of years, over a population of 320 million, AND included justifiable homicides (police shootings, self-defence, etc.)
try arguing against that fact instead of posting up mis-informed rhetoric.