No, I don't pre-suppose that he is a racist, but he did drop a stereotype into the discussion, which led me to suspect him of sloppy thinking. The idea that Muslims are more misogynist than, say, Promisekeepers, doesn't hold much weight. It rests primarily on the conflation of militant, fundamentalist Islam (which is undeniably, and horrifically, anti-woman) with other, more mainstream and "assimilationist" varieties of Islam. There are anti-woman passages in the Koran, just as there are in the Christian Bible, the Torah, and the primary and secondary texts of many other religions. But in our current political climate, many people are more likely to identify Muslims with anti-woman attitudes than they are to identify Christians, Jews, Hindus, Buddhists, etc. with the same views. The horrific suppression of women by the Taliban became front-page news after 9/11, when the country was being maneuvered into a war against fundamentalist Muslims; the practices in question (capital punishment for adultery, mandatory burkas, denial of education, the list goes on) had been in place for many years, but had received minimal press coverage. As our country maneuvers its way into more conflicts with Muslim nations, many people are more than willing to speak to the plight of Those Poor Beaten Muslim Wives, not because they particularly care for the women in question, or for the issue of domestic violence in general, but because it is a way to claim an "altruistic, noble" position while simultaneously giving voice to popular anti-Muslim sentiments.
It's worth noting that I do think DavidOdden has a good point - cultural relativism does encourage us to suspend judgment of domestic violence in Muslim families (along with similar crimes, such as dowry murders in India, and female genital mutilation in some African cultures). If Inspector had bothered to expand and support his "Muslim beating his wife" scenario, incorporating David's ideas, I probably wouldn't have bothered to question his use of the example. Many people do use cultural relativism as an excuse to overlook atrocities, and that's horrible.
However, in Inspector's original statement, the use of casual stereotype ("wife-beating Muslim," which is on a level with "dumb red-stater," "criminal black," "heartless, greedy industrialist," etc.) seemed like evidence that he had not thoroughly examined his premises, and that he had simply regurgitated popular views into the discussion without examining them fully. I have no personal interest in Inspector, but it seems to me that a philosophical discussion can only benefit if the participants are willing to point out perceived flaws in each others' logic.