https://www.abc.net.au/news/2021-05-27/victoria-lockdown-restrictions-on-masks-gatherings-travel-school/100169450
Because you got in before the mandatory hotel quarantine time, but according to the ABC news yesterday you have to behave just as if you were in Melbourne : in lockdown at you accommodation. (I had a look at the Qld health site and it looks like they’ve messed up their 1.00ams. But I reckon they will fix that. You were also supposed to have been met at the airport and told what to do. According to the news)