There isn't even an accepted definition of intelligence in humans, let alone animals, never mind machines! We're pretty much at the "I know it when I see it" stage of definition.
How can that be true? If the author is doing AI research presumably they and others in the same field have have some foundational shared ideas that they build upon. If they didn't how would a person earning a PhD in this field ever be able to say if they are contributing something new to the study of AI? There has to be something that defines the work as work in AI rather than just computer science.
A large foundation for this field is statistical inference. To me, AI almost always means ML, and ML = algorithms that optimize themselves to make predictions.