I left this question in literature given your tagging of McKay's novel Charlie Wilcox although your question could easily be moved to reference given its context.
There are many times in life where one listens to another person without actually hearing what is being said. As an example, which can appeal to both teachers and students alike, imagine a classroom. Within the confines of a classroom, teachers present large amounts of information pertinent to the unit/lesson being taught. While the teacher may talk for an entire period, many students may only be hearing and cannot recall a single thing the teacher said. This happens when a student is not focused upon what the teacher is saying; instead, the student only hears that the teacher is talking. When asked questions about what the lecture was over, a student who only heard the lecture, but did not listen, cannot recall the information.