He was not just a nutter with a knife, he was a nutter who built a fake bomb and brought that and a knife to the terminal with the aim of threatening people. In light of that, I do not think that the police over reacted.
From
https://www.abc.net.au/news/2019-02-...ice-1/10775238
The police treated the threat so seriously that they even locked down and searched a car park and apartment block an hour away (probably where the perpetrator lives).