Trying to summarize a half-remembered book, but the big revelation is that the aliens are not sentient at all. They are rather operating on instinct. The point of the book was more to discuss the nature of being human and is consciousness/sentience all that necessary. Lots of philosophical waxing on the nature of thought.

As to your question about other species, I think you are posing a rather challenging problem. How does an author write from the perspective of a being significantly more intelligent than themselves? Their actions and motivations become wholly alien as comprehension is not within our reach. One can justify any alien action as the unknowable motivations of a capacious god.