Sometimes friendships are more important than winning an argument. Let's say that his friend is passionate about, say, tennis. She knows all about different types of serves, which angles to take, etc., but to him, it's merely a nice way to spend an afternoon.
She could spend her time trying to persuade him to become a serious tennis player--or she could simply appreciate the fact that he likes playing tennis, and that they enjoy each other's company. If she needs to talk about the fine points of tennis, or play at a high level, there are plenty of clubs where she could find high-level opponents--but if she browbeats him for not playing 'correctly,' she's likely to make him lose all interest in tennis, instead of making him a better player.
As for Ozle--if his point was to say, 'She's a girl--girls are stupid and don't get Dominion'--then of course he would be sexist. But if his point was, "She's a girl who likes spending time with you--don't blow it over a stupid argument" then his reply was spot-on, and much shorter than mine, which for most people will be tl:dr.