South Australia state Premier Steven Marshall said at a media conference in Adelaide that the man who tested positive told contact tracers he had only bought a pizza at a pizza shop, when he had actually worked several shifts there alongside another worker who tested positive.
A cluster of infections in a northern suburb of the capital city of Adelaide has seen more than 20 cases.
Pieces of that person's story "didn't add up", he said.
Mr Marshall said the man was one of the cases linked to the Woodville Pizza Bar, and told authorities he was a customer.
"The selfish actions of this individual have put our whole state in a very hard situation".
'His actions have affected businesses, individuals, family groups and is completely and utterly unacceptable'.
"The Emergency Management Act requires people to provide information on request", he said.
Marshall said: 'One of the close contacts linked to the Woodville pizza bar deliberately misled our contact-tracing team.
"If this person had been honest with the contact tracing teams, we would not have gone into a six-day lockdown".
Under the roadmap's plan, people will be allowed up to 10 people at their homes.
Religious ceremonies will return but also be capped at 100 people, while all other private gatherings will be capped at 50 people. The residents are also not allowed to step out for their daily exercises or for even walking their pets.
Masks are mandatory for hairdressers and beauty therapists but residents will no longer be required to wear a face covering when in public.
A government spokeswoman on Friday confirmed the state will begin receiving worldwide arrivals from 7 December, with an initial cap of 160 travellers per day.
The state's outbreak follows neighbouring Victoria's success in crushing a second wave of coronavirus which caused about 800 deaths.
"This person has numerous associates, persons of interest that we are now trying to identify and locate that we would not have had to do so had they been truthful from the beginning", said Stevens.
There are two just active coronavirus cases remaining across Victoria, according to figures released by the health department on Friday. However investigations continue into a weak positive test result that may be a case of virus shedding.
There have been three new cases of COVID-19 in South Australia today, however all were already in quarantine.
Both locations are along freight corridors, and the results emerged amid Adelaide's growing cluster, which has sparked a six-day "circuit-breaker" lockdown over the border.
The authorities have asked people to stay indoors at all times. Check your jurisdiction's restrictions on gathering limits.