You couldn't possibly have known that's what it was for, but maybe next time, be more general when asking what the loan is for because you never know if its for something good OR bad.

^ This. Couldn't have known, but it's a learning experience. Just like in retail, don't ask why someone is buying/returning certain items. (Example being returning baby clothes or diapers) People blurt things out dealing with grief. The couple who you asked could have said something else as an explanation until they got with a banker and started filing. Don't feel too bad, but keep it neutral next time!