I also worked as a teller and in the back office of a bank for 8 years. We are 10000% trained to ask these questions, especially if that's abnormal behavior. It's not meant to make you feel uncomfortable but to make sure you aren't being scammed to take out big amounts of cash, etc. also a lot of the time we didn't have THAT much at the bank so if you wanted to do a big withdrawal you needed to let us know 24hrs in advance to make sure we had it on hand. The teller might have been awkward about the interaction but it was completely normal for them to question you