My bet is that the standard applied varies based on racist and other tribalistic (if different) sort of prejudices held by the relevant individuals making judgments about what is acceptable and not.

If a person's proof of identity and citizenship document is held as valid by the issuing authority of a recognized foreign country -- no less so when dealing with an easily verifiable epassport at that -- asking a person seeking admission about entitlement to citizenship and the passport related to such citizenship comes up way more frequently when dealing with those applying racist and other prejudices (rooted in ignorance) against minorities -- whether those minorities be visitors to the US or even US nationals/citizens.

My bet is that the US CBP employee knew full well that this Australian citizen had a valid Australian passport with her face easily matching her photo. Or is the CBP employee involved at the start going to claim blindness? It's not like that CBP employee would be able to credibly claim blindness to the ethnic and birthplace heritage of the visitor.