This is definitely work experience. Teaching is not easy, and it is especially interesting how/where you conducted your teaching. I think that you could craft an excellent story!
Adcoms can look at this experience many different ways. They are going to want to see why you did it, and where you want to go in the future, and how an MBA is going to help you. If you can put together a great story, I think your non traditional background might even be an advantage. It all depends on where you want to go in the future, and how well you craft your essays.
But to answer your main questions, YES, teaching would be considered work experience. I also think that since you were teaching economics, this is an important factor b/c economics is directly related to business. This is another way you can show you interest in business even with non traditional work experience.
As a banker myself, I can tell you that Adcoms are not looking to fill there classes with 100% bankers or consultants. The non traditional applicant has their spot in the class too. So make sure that one of those spots is for you!
New to the GMAT Club? <START HERE>
My GMAT and BSchool Tips: