No, it doesn't "prove" anything. One can assume it's proof, but it isn't proof.
Semi-auto pistols, not rifles, are the most common tool for shootings here in the US. So there is no reason why they couldn't have been used to commit shootings in Oz as well. So if they're legal in Oz, then it's just a statistical anomoly that no shootings happened.
Unless a rifle has a big clip, it has no advantage inside a classroom over a semi-auto pistol. In fact the pistol has an advantage because it's easier to conceal.
Semi-auto pistols, not rifles, are the most common tool for shootings here in the US. So there is no reason why they couldn't have been used to commit shootings in Oz as well. So if they're legal in Oz, then it's just a statistical anomoly that no shootings happened.
Unless a rifle has a big clip, it has no advantage inside a classroom over a semi-auto pistol. In fact the pistol has an advantage because it's easier to conceal.