It's explained @ ~around the 35' minute mark, but basically he did not understand or grasp metaphors, https://en.wikipedia.org/wiki/Conceptual_metaphor - like a machine he would interpret everything literally, excellent case study for some of the obstacles facing AGI in my opinion.

> Conceptual encoding contributes to the construction of conceptual representations in the mind of the addressee, whilst procedural encoding provides the addressee with instructions as to how conceptual representations are to be manipulated to achieve relevance.

To me it reads as a lack of ability to conceptualize, for instance, others‘ state of mind.