I mean there's that, but also it's well known to Australians that their government has sold them out to be a client state of the US. On trade, allowing American military bases on the continent, and more.
We are a US puppet state that constantly tanks our economy to please our American overlords. Some people pick up on that, despite the constant right wing propaganda shoveled down our throats.
Others hate the US because like most Anglo countries, we compare our how hideously incompetent government and cruel, callous society to them. It's a societal get out of self improvement free card. "We might not be perfect, but at least we aren't as bad as America!"
yeah but it's not rooted in some principled stand, it's because we're the funhouse mirror that lets other genocidal settler colonies (or the genocidal mothership herself) off the hook for as long as we're around. "oh no, the mean americans are making me do a genocide again, oh no"
death to america by all means but let's not pretend most of the australians marking "disapprove" didn't do so because the nasty seppos with the school shootings make them feel better about their own settler violence
We generally don't like Americans as a group, but will bend over backwards to say how our individual yankee mate from uni is actually a decent person if you get used to them. It's more from a sense of cultural inadequacy than actually having any cogent objections to the American empire (for the average person it's posited that America may be a big bully but they're our big bully against the inscrutable *rientals)