Precision and recall clarification
It's very likely that the authors assume that the spam class is positive, whereas you intuitively associated the ham class with positive. Both options make sense in my opinion:


the former interpretation is based on the idea that the goal of the task is to detect the spam emails, seen as the class of interest.
the later interpretation considers that the ham emails are the "good ones", the ones that we want, hence the "positive" class.


There's no error when one reads the paragraph with the authors' interpretation in mind. This confusion illustrates why one should always clearly define which class is defined as positive in a binary classification problem :)