Given all the rumors (and that is all they are at this stage) that the "Avalon Cluster" was started by a returned crew member
That's all it is, a rumour. The Health Minister said that they do not believe that is the case. They could easily track which crew have operated in, where they live and access their day 12 COVID test result.
Additionally, genomic testing has shown it is highly likely the infection arrived from the US. Now take a look at who flies to Australia from the US. The only service that Qantas operates is a single weekly LAX-BNE freight service crewed by BNE based pilots. So while there may be many Qantas crew living on the northern beaches, none of them are flying to the US where this particular cluster has seeded from.