The 480,000 is the bare minimum. 50,000 - 250,000 is a loose number based on assumptions of 1%
So for example if 40% of Australians contract the virus and 2% die then around 180,000 die. Take into account our better health system and the figure drops to around 50,000. That's if we do enough to slow the impacts.
If 40% of the world is infected and there's no slowing of the virus then the death rate is over 600 million. With solid attempts to stop the virus, strong quarantine measures, etc, then it could drop down to below 500,000.
That's based on projections with a 2% mortality rate. The WHO is now saying that the mortality rate is closer to 3.4%
But there's different projections from different groups and we don't have enough information to accurately predict it yet. For example, Harvard Epidemiologist is saying 40-70% total infection, while others are saying less or more
https://www.businessinsider.com.au/...illion-adults-harvard-expert-2020-3?r=US&IR=T