You must have misunderstood the assertion, then. I will attempt to clarify.
- Australia tried to get rid of guns, still has millions. Several hundred thousand of them illegal.
- Australia has a much lower firearms homicide rate, despite still having quite a lot of guns. Not the same ratio as the US, sure, but 4.5M guns for 28M people is still fairly prevalent and available.
- So the rate 1:50 ratio is not easily explained by simply reducing the number of guns in circulation. Something else is going on. Something harder to solve, even, than the second amendment.