Once upon a time, I forgot my password. I called tech support to get my password reset. The nice young lady did the reset, gave me a temporary password and told me I would have to change to a new password once I logged on. She then told me that I couldn’t use my old password. I asked, you mean I can’t use the old one, the one I forgot? And, she replied, yes, you can’t use that one.
she is correct. perhaps you had yours written down and found it after hanging up. or you hung up, remembered it and wanted to continue using it. so this could just be a reflex answer. when i go through the drive thru and ask for a black coffee , sometimes the response is "do you want cream?" but i think it's just a response to asking for coffee.