Banana cupcakes? Muffins?

What is the difference between a muffin and a cupcake? Is it really just the frosting? I was reading an old issue of Bon Appetit and saw this recipe for banana cupcakes with peanut butter frosting. It really just is banana bread in muffin form with a good serving of peanut butter cream cheese frosting. Maybe by calling it a muffin it's less caloric? Regardless, it was delicious and I would make it again.