Well, I find nothing offensive about that, ssprengel. A Mac user who writes MAC is simply beyond comprehension, unless that person happens to be a rank beginner and a newbie Mac user. There's no offense meant, and none should be taken—unless the person is deeply embarrassed by the faux pas that she feels compelled to insult the user trying to help.
If that had not been my firm belief, I would not have referenced.
…and of course we must remember that you're not a Mac user, at least not primarily.