Clarification of textbook concepts relating to "perfect", "ideal", and "real" gases
The authors attempt to explain that in many sources the term "ideal gas" is used in place of "perfect gas" to indicate a gas following the ideal gas law and which has the property that the molecules do not interact. They equate the absence of an intermolecular interaction with the statement that the "interactions are zero". In other words, there is no intermolecular potential between the idealized gas molecules in a "perfect gas". These idealized molecules lack a volume, so that even steric (excluded volume) interactions expected for hard spheres are absent. They are "point particles".  

The authors further explain that it is preferable to use the word "perfect" rather than "ideal" because the word "ideal" is used in other contexts where the condition of no interaction is not observed, ie during ideal mixing. Ideal mixing occurs when different molecules have the same volume and intermolecular potential in the pure and in the mixed states.



Opinion-based aside

BTW I've always been partial to the term "ideal gas". IMHO the term "perfect" seems to imply that the molecules excel in some way, whereas "ideal" simply means that it is the product of human minds, an abstraction, and not necessarily a real thing.

IUPAC does not to have any qualms about continued use of the term "ideal gas", so I don't see reason to stop using this term.