Why would this girl in Australia think me not knowing what her "living in the CBD of Sydney" is the craziest thing?

I'm from the US. If I told people I live in the CBD of a random US city, the vast majority are not going to know I mean "Central Business District".. She acted like this was the craziest thing to not know.

Why would this girl in Australia think me not knowing what her "living in the CBD of Sydney" is the craziest thing?
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