Yep, Carbon is 9 or X, Cocoa is X only.
CarbonLib is the OS 9 extension that's used to run Carbon apps. Delete CarbonLib from your system, and you won't be able to run Carbon apps in 9 any more--it provides the Carbon API for OS 9.
Just to make things really confusing:
There are three kinds of apps you can run in OS9: CFM68K apps, InterfaceLib apps, and Carbon apps. There are three kinds of apps you can run in OS X: Carbon apps and Cocoa apps, which use the GUI, and BSD apps, which are Unix programs that are command-line-only.
If you add X11 to your OS X system, you can now run four kinds of apps in X: Carbon, Cocoa, BSD, and XWindows. XWindows apps also use a GUI, but it's not the Mac GUI, it's the XWindows GUI.
There'll be a quiz on all this stuff next Tuesday; remember to bring a pencil...