The more I look at the article and that line, the more I think that the comeback isn't the "it didn't occur to me" but the "X and Y behaviors don't seem ethnically specific." The author gives a specific reason that ethnic issues didn't occur to him/her (Dana?). It's not just a blanket "It didn't occur to me so it's not there." I read it as "Nothing I saw was remotely ethnostereotypical, so it didn't occur to me."

Is the alternative that we assume every action we see in a movie probably stemmed from some stereotype that we aren't aware of yet?

I think that article is right on target about the relationship of the movie and its characters to women, btw, having gotten a chance to read it more closely.