Amazon calculates a product’s star ratings based on a machine learned model instead of a raw data average. The model takes into account factors including the age of a rating, whether the ratings are from verified purchasers, and factors that establish reviewer trustworthiness.
The GUIs shown in the book and the ArcGIS Online account that available commercially are not the same. The app template in the first lesson wouldn't open at all. I got this same book from the class I took at ESRI a few weeks ago, provided by the instructor. I don't know if its out-of-date or what the problem is, but try it first and be prepared to return it.