Reducing guns in Australia may have been the sole cause of the change. I doubt it, but maybe.

Being in poverty makes people more likely to commit suicide, but wealthy people commit suicide too.

Men are much more likely to kill themselves than women, but women still kill themselves too.

But maybe the same changing attitude towards gun rights was part of an overall shift in the culture of Australia that also lead to a decrease in suicides. How does one quantify changes in culture though? I mean, other than the 10 or so ways I've already suggested.

And if every other variable that I think may contribute to suicide was wrong, and suicide rates are directly and only tied to guns being around, then how do you account for countries like Japan and South Korea having such low rates of private gun ownership, yet such high rates of suicide?

These questions lead any thinking person to conclude that suicide may be more tied to the overall culture of the country in question, not strictly the access to firearms.