I haven't read the book, but am somewhat familiar with the case as it appears in many texts that I use. My take on the case is that it is evidence for biology being the primary determinant of one's sex, male or female.
Biology especially includes the brain.
Regardless of our secondary sex characteristics, it is the brain and biology that determines our sex. The roles associated with being male or female, our gender, are socially constructed and derive largely from culture. The ideological point being that biology is destiny.