An entirely intelligible response to a hegemonic culture with substantial overlap with your own: fear that your culture will be assimilated into the hegemon, that the country will become unrecognisable to you, that the virtues you are familiar with and have come to cherish will be eroded. That you will cease being you, and start being the Other.
In the panoply of worldwide reactions to hegemony, this one’s rather on the benign side. It’s not Trumpism. It’s not Sinophobia. It’s mostly jocular. And I’m sure it’s exactly what happens in Canada too—except that Canadians are much more polite about it than Aussies are.
(Except possibly for the Québécois, câlisse!)
You might wonder why Australians weren’t as overtly hostile about their former hegemon Britain. But there were flareups, even back in the unenlightened days before Gough Whitlam. The Bodyline tactics in cricket in 1932, leading to Australians boycotting UK products. The strain of Australian nationalism of the 1880s and 1890s, hosted by The Bulletin. The class and sectarian war behind the idolisation of Bushrangers.
Some of my best friends are Seppos. But don’t tell anyone, OK?)