This article has some huge issues.

As mentioned already, the type of gun matters a lot. No mention of how many are semi auto, but I am guessing it won't be many.

Also no accounting for population growth over the last 30 years as a factor in total gun numbers.

This paragraph was absolutely journalistic garbage.

"NSW firearm registry data shows that in Sydney there are more than 70 individuals who own more than 100 firearms, including one person who owns 385 guns. The register notes that this is not a collector or a dealer."

Clearly this is a hobby/interest and the person is a collector with too much time and money (good for them I guess). What they don't have is a "collectors" licence that effectively means they cannot ever use their guns. A licenced collector will usually have inoperable firearms on display (think museum).

All that said, the SSAA and others do have a higher than normal concentration of right wing nuts that continuously lobby the government to weaken our excellent (imo) gun laws. It's why I stopped giving them any of my money.