Hello Abhinav,
You are correct. These topics are indeed not in the PMBOK Guide, but they are part of the PrepCast. This is because the PMP Exam is NOT a test of your understanding of the PMBBOK Guide. Instead, the PMP exam tests your knowledge and experience as a project manager.
Please review The PMP Examination Content Outline:
www.project-management-prepcast.com/pmpoutline
This document describes all the topics that you will be tested on during the exam. You will notice that many of the topics in the Outline can also be found in the PMBOK Guide. But the Outline has additional topics (like benefits realization) not covered in the PMBOK Guide. And while The PM PrepCast generally follows the structure of The PMBOK Guide, it does include all the topics from the examination content outline.
So if at any point you come across a PrepCast lesson where you cannot find a specific chapter in the Guide then that means that the topic is part of the Outline.