The paragraph after Definition 4.3 in Chapter 4 is:
A test with a significance level of $\alpha = 0.05$ will have a false positive/type I error rate no larger than 0.05. This level is widespread in the social sciences, though you also will $\alpha = 0.01$ or $\alpha = 0.1$. Frequentists justify this by saying this means that with $\alpha = 0.05$, there will only be 5% of studies that will produce false discoveries.
This should instead be (with differences in brackets []):
A test with a significance level of $\alpha = 0.05$ will have a false positive/type I error rate no larger than 0.05. This level is widespread in the social sciences, though you also will [see] $\alpha = 0.01$ or $\alpha = 0.1$. Frequentists justify this by saying this means that with $\alpha = 0.05$, there will only be [at most] 5% of studies that will produce false discoveries.
(a missing "see" word and an addition of "at most" to make the last statement more precise)