"The cafe owner has allegedly contravened a public health order,...

"The cafe owner has allegedly contravened a public health order, by failing to comply with the Public Health order. That is not a law."

He has failed to comply with the Public Health Act Part 3 section 21, which is the law stating you must follow public health orders.
It is the law that makes it an offence not to follow a public health order, and is the legislation that covers it.
https://www.legislation.qld.gov.au/view/html/inforce/current/act-2005-048#ch.2-pt.3

Do you really think you can be fined and sent to jail for not breaking a law , LOL

As they say, ignorance of the law is no excuse.