The lesson for the publisher seems to be: always double-check the data; and if you don't understand what exactly they mean, ask an expert.

No in this case the publisher made a lot of money with the book.

I am not sure what exactly is the lesson here. This is one data point, but what is the proper generalization?

Case studies are a good tool to understand things on a qualitative level. The value of a case study doesn't depend on whether you can generalize it message into a single sentence.

If you want a one sentence generalisation you however could go with: "Books become best sellers for pretty random reasons that have little to do with quality of the actual book."