When I was traveling in Mexico, it drove me nuts that even though I was signed in, Google Flights switched my currency from dollars to pesos every single time I opened a new tab! I think they really don't care.
I think they rely on ip for a lot of stuff they shouldn't. Getting a local esim switches me to km until I switch back to my old one. Have no idea about Australia.
Edit: after typing this realized this isn't ip, its provider. That maybe does make sense to cue off of.