As someone pointed out below, the stat is very likely misreported. However, I also question what is meant by "book" because while most of the fic I read is short enough not to qualify, some of them are book length. What's more Kobo tracks each file as a "book" and if that's the case I read around a dozen books a week. If people are reporting files as books as they may when using mobile devices to read, then it wouldn't surprise me at all if the reading statistic is far higher than has been counted in the past.