You will, however, probably need some background information if you are to make sense of the examples, background information that you are unlikely to have acquired in the law courses that you have studied up to now. Procedure is how the law works, and a knowledge of that is far more important to a lawyer than knowing what the law is. By that distinction Restitution is clearly procedural.
Restitution is about how one gets something.
On the other hand, many of the cases in this book do involve Contracts or Torts. That's not the problem. That is the kind of real problem that real clients care about. And that is one example of one of the many problems that we study in a course in Restitution. But Restitution is not particularly about contracts.