He has a convoluted (no pun intended) center of mass explanation that the equation does not describe, admits that this is incorrect, and then goes onto another incorrect explanation of a strange ellipse where there is another center of mass.
I've never been able to find a good explanation online, only in some older textbooks. I've begun to fear that there are few people who are able to read equations while the others interpret the explanations of those people, where then those same old explanations gradually mutate as they propagate without reference to their source. This Stanford lecture is the best I could find: https://www.youtube.com/watch?v=1rqJl7Rs6ps
I've never been able to find a good explanation online, only in some older textbooks. I've begun to fear that there are few people who are able to read equations while the others interpret the explanations of those people, where then those same old explanations gradually mutate as they propagate without reference to their source. This Stanford lecture is the best I could find: https://www.youtube.com/watch?v=1rqJl7Rs6ps