Outdated in what sense or how?
Thinking as Computation was developed from a course meant to introduce first-year students, from a wide variety of disciplines, to the topic. The prerequisites are thus very light and require little more than high school mathematics and no programming experience.
The author directly describes the scope and context of the book in the preface, and it was primarily designed to give students hands-on experience on the topics. Prolog turned put to be a successful choice in teaching students with no programming background and helped guide the course material.
The book isn't really an introduction to AI, although the topic lies within the larger umbrella of AI.