I don't think it is Callistemon. We would probably find more if everyone was randomly screened (impossible I know).
I think it must prove extremely difficult to locate, or even be aware of every single and casual contact, and as I mentioned before, many may be symptomless, or have minor symptoms.
Many of us travel through hubs such as airports, stations and busy urban sites.
I dont feel too alarmed or anxious, the majority of us by the law of averages, even oldies, will be ok. It makes sense if you have risk factors, to avoid crowded areas where possible. Thankfully children seem less at risk.