(Sorry if this is not the place to report this)
The description for chapter 2. UIKit & The One-Button App is:
You’ve built two apps using SwiftUI, yay!. In this chapter, you will start building Bullseye using UIKit, Apple’s existing way of building UI for iOS apps.
Probably this is a leftover of the chapter’s reorganization, I seem to recall that in a previous version SwiftUI was presented first. A minor error but can be confusing for beginners.