Not surprised by the questions from the bank. They can get in deep crap if their find out is money laundering or for other illicit activities.
I made request to withdraw $15k from a credit union to buy a used car for the kids years ago. They guy wanted cash. The credit union said, they needed a day because it would wipe out their branch reserves but I could go to the central location if I wanted it today. No big deal.
They did ask what it was for. The teller said something about being required to ask per federal regulations for any large withdrawals. I don't know if he was making that up or not but it made sense since they are required to monitor for money laundering.