You call it rambling others don't. Perhaps its more about ideological outlook than content.
He starts with the posture as this is the physical manifestation of the mindset at least for those who don't have any physical disabilities. But we know that psychology is behind many physical manifestations. He then elaborates how this is related to mind, the psyche. This is psychology 101.
Body Posture Affects Confidence In Your Own Thoughts, Study Finds
The results show how our body posture can affect not only what others think about us, but also how we think about ourselves,
Sitting up straight in your chair isn't just good for your posture -- it also gives you more confidence in your own thoughts, according to a new study. Researchers found that people who were told to sit up straight were more likely to believe thoughts they wrote down while in that posture...
www.sciencedaily.com
Heads Up! Good Posture Helps Both Your Mind and Your Body
Slouching can be hazardous to your mental health as well as to physical health.
Would you like a simple way to look better, feel better, and improve your mood? Practicing good posture has both mental and physical health benefits.
www.psychologytoday.com
Well I am not sure why else you would make this objection. Perhaps you take a more a reductivist and behaviouralist view that everything is conditioned or physically caused.
But the point is these are not simple questions. To say that they are is perhaps the problem. Expecting a simple answer to a more complex issue is unreal.
No I don't think he is avoiding any answer. I mean this is an either/or fallacy that people must answer yes or no to whether they believe and if they don't answer clearing with a yes or no they are avoiding the answer.
For some it is a case of they are just not sure, agnostic and have a more nuanced answer.
Well your dislike comes through. It seems more than just his content and more a personal difference.