Wolf:
It is accepted Minhag among Chassidim to not have spouses eat with them when they have men over at their house (as I have seen myself). I would assume this is a similar concept.
It may not be “halacha”, but we never like dismissing Minhagei Yisroel.
His wrong was saying it was “Halacha” instead of a Minhag/Chumrah. This is a very common error (as I am sure you know), and I have seen this not only by Tznius, but also G’Brokts, eating in the sukkah on Shmini Atzeres, and Shkiea/Tsais (as well as others).
May we all be Zoche to “have all of Tanach, Shas and Rishonim at my (and our) fingertips”.