Hi, if possible could you link to the nature communications article, I would like to read it.

The bigger brain= more intelligence rule works well within a taxonomic order. For example, humans have much bigger brains than other primates and are more intelligent. However when you’re comparing species from different orders the rule doesn’t work very well. The brain of a giraffe is almost twice the size of an orangutan brain, but the orangutan is thought to be much more intelligent.