There’s a fair bit of context absent from this article. The military aren’t being deployed to enforce a lockdown so much as they’re providing some extra manpower to augment the local police force. NSW Police have part of their workforce isolating due to exposure to infected people, coupled with extra patrol requirements, and they need some more bodies.

The military personnel will be unarmed and will be accompanied by police. The army doesn’t actually have any powers in this scenario, so it’s up to the police to actually issue fines, make arrests, move people on, etc.