The textbook authors recognize that the resistance is already present in the bacterial population (Fig. 15.5) and then claim that selection for resistant bacteria in a population is direct evidence for evolution. Selecting for something that is already present does not provide support for the information-gaining change required for evolution. Students are left with a confused understanding of evolution and are expected to equate observed changes in bacteria with the conversion of one kind into another.
See Evolution and medicine for more on antibiotic resistance. http://www.answersingenesis.org/articles/am/v2/n2/antibiotic-resistance-evidence