Group A credits relate directly to activities in the areas covered by the specific domains of the respective credential.
Group B credits are earned for completion of general professional development activities which enhance your overall professional skills, education, knowledge, or competency outside of the domains associated with the respective certifications.
So, to answer your question with a question, how comfortable would you be defending the work of fiction as "relating directly to domains" or as "professional development"?
"To fulfill CPE requirements for CISSP, can we read fiction books related to cyber security?"
Would you be OK with your lawyer reading John Grisham books to meet continuing legal education requirements of the Bar, or your doctor reading Tess Gerritsen books for requirements of the state medical licensing board?