[LKK]

One thing to remember in this discussion of what is and is not supernatural is that the Japanese are more likely to consider things to be supernatural in origin than most Westerners. They tend to be more superstitious than Westerners as well. Yes, that's a broad sweeping generalization about a large group of people, but anime often uses broad sweeping generalizations to fill in the explanatory gaps in its logic. Keeping this generalization in mind, it's easy to understand why the librarian attributed the teacher's death to the phenomenon so quickly and absolutely.