How can my app have more updates than apps sold, by a significant amount.

I make educational apps and here and there I see updates on one day in the numbers of like 15,000 updates IN ONE DAY. Needless to say I never sold that many app to even have that many updates. I mean, one of my apps sold maybe 1,000 copies but yesterday we had 16,000 updates from Canada. How is that possible? What is going on? These are all paid apps.