The notice that goes out when you ship is not part of the normal Etsy messaging system, it is a processing message sent by Etsy. If the buyer answered that, their message goes through to your inbox as an initial contact from the buyer. You have to reply to that, or mark it as spam within 24 hrs or it will be counted as not replied within 24 hrs. You can try marking it as spam now and with luck it will update your stats in time for the Jan 1 badge assessment, but updates can take a day or two, so it may not get through in time. For the future, any new message in your inbox that has a blue prompt saying something like "First time making contact" requires a response within 24 hrs.
