Try some searches (
www.google.com/trends) on all kinds of other things--current Christian writers, past Christian writers, Christian publishing companies, historical figures, political leaders past and present, etc., and Tomes' statistics may no longer appear to be so significant.
Here a few tests I ran: Lee Strobel, Norman Geisler, A.W. Tozer, Zondervan, Harvest House, Kregel, English Standard Version, Doubleday, Penguin Books New York Times, Ralph Waldo Emerson, Booker T Washington, Calvin Coolidge, Tony Blair, Obama.
Others appear to be having the same problem...