[papercrane]

In the US any cash withdrawal that large triggers a legal requirement for the bank to file a transaction report with the government. If the teller didn't ask you anything and you don't regularly make withdrawals like that then somebody messed up.

[RandomBacon]

As far as I can tell, they are only required by law to ask for identification; no requirement about asking why. The report they make goes to the IRS where the IRS might ask a question.

https://finance.zacks.com/federal-banking-rules-withdrawing-...

The teller asked for identification which exactly what the law requires, so it doesn't sound like they screwed up.