Of course there are ads. Amazon never implied that there wouldn't be. This isn't Amazon trying to be sneaky. The opening lines say that everything is free and developers get paid according to use. How did you expect that would happen? It has to be subsidized in some way, and in the context of an app store that means ads.
When you download an app in the app store it says "free" not "free with ads" because you don't have to pay any money for it. It's still, technically, free.
When you download an app in the app store it says "free" not "free with ads" because you don't have to pay any money for it. It's still, technically, free.