There are no such things as "stupid" questions. However if you think your question is a bit stupid, then this is the right place for you to post it. Please stick to easy to-the-point questions that you feel people can answer fast. For long and complicated questions prefer the other forums within the support section. Before you post please read this
Was one of the packages updated in the first update mintupdate? Sometimes they change something about the repositories, that change is reflected in the next mintupdate, and once you've updated mintupdate, you find out about all the other updates you've been missing because they were at a new place. That doesn't happen often, maybe once every year or two.
Whether it's this scenario, or the more likely one Crewp described, this doesn't happen very often.