As I mentioned, it could a possible second case based on the times and the geography.
First case was at say found o be positive at say 10 or 11-ish AM. He was being interviewed while the presser was on.
They do use the rapid test for close contacts where they are known to have had close proximity to the index/new case, as well as the slower PCR to confirm as it is more accurate, in order to speed up find positive in close contacts such as workmates or household contacts.
That initial screening with the rapid test may have discovered for example a positive co-worker, who say lives in Altona North and who stopped off at the Yarraville 7-Eleven on the way to work..
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Remember that the first case found today, may not be the first case in whatever this cluster ends up being. The case announced this morning was symptomatic. He may have positive asymptomatic contacts that infected him, or vice versa.