KRviator -
Why not quote the rest of the article that you link?
"Asked by Commonwealth Solicitor-General Stephen Donaghue QC if his advice to keep the border closed was based on an assumption he had to work on and all-or-nothing approach, Dr Robertson agreed "
“But the other risk is that you would then become dependent on the decisions of another state for them opening their borders, so if they opened their borders, then people could pass through the state into your state without restriction.”
Despite the small risk, his advise is to remain closed.