It is believed that Lewis is referring to the "Word of Wisdom" with the word “teetotalism.” And while I wouldn’t call that irrefutable proof that Lewis wouldn’t have joined the church if missionaries had knocked on his door, there is plenty of evidence that the Christianity C.S. Lewis believed in and the Christianity Mormons adhere to are incongruent.
Sophia L. Stone is the author of Mormon Diaries. She's a seeker, learner, reader, and nature Lover. If you're on twitter, you can ask her any question about Mormonism @ask_a_mormon