Is it reasonable to call using that which is freely given "stolen"?
Think of this like a college atmosphere if you will. If a student takes data from a book, an uses it in a study or a paper. At the end of the paper they are required to say where they got that data from right? Even in a learning environment where laws are a little more, but not completely, relaxed you find that its extremely important to note the source. This is in "educational" use.
This really comes down to two things. Fair Use breaks things down in to two categories. For Commercial Use and for Nonprofit Educational Purposes. Something I won't touch on, but is also considered is the potential market value. But looking at commercial vs nonprofit educational value. When you take the work of another company, and put this in to an app where you are making money be it promotionally, or customers are paying for the app. Then yes, you are stealing.