No, seems to me that giantrobot's point is that adding randomness to port numbers is a light security through computational complexity (almost a shared secret),

No, seems to me that giantrobot's point is that adding randomness to port numbers is a light security through computational complexity (almost a shared secret), that can in turn be used to help prop up other security practices, such as fail2ban. Security through obscurity is reliance in security engineering on design or implementation secrecy