That's correct. Going further, the poster you quote thinks it's permissible to have all female gatherings because of intrinsic disadvantage suffered by women, but not all male gatherings because there's no intrinsic disadvantage suffered by men.
Whatever the ethical issues, that position is not the law. Both all female gatherings (societies) and all-male associations are legal. In each case the association is restricted to members who share a protected characteristic (being women or men respectively.)
More widely, except for the section on affirmative action, the Equality Act 2010 forbids discrimination in both directions; treating someone either worse or better on account of a protected characteristic is unlawful (except for the PC of disability - see section 13(3)).