This code is completely orthogonal to what OF is doing. This code is plugged into your "empty example OF app" by adding the class and declaring this class as the application class in AndroidManifest.xml. OF doesn't touch this part at all. OF starts working when the OFActivity class is created and comes to the foreground. OFActivity is the android part that hosts the openGL view that does the drawing you do in the cpp part. This will still happen as usual (because the OFActivity is already defined as the initial activity when the app is started). Notice that in the guide there are also steps that require changing the activity (handling the different buttons like home and recents). You will need to change the existing OFActivity.java class.
And regarding required java skills. Even though OF usually abstracts java/android stuff away from you and you can create apps by just modifying the cpp side, what you are trying to achieve is very much at the java part, so I see no way around it (other than if you or someone else will pick up the towel and build android kiosk mode directly into OF core). So if you want to brush up on relevant parts of android, I would start on the page about the activity class, especially the methods that are being overridden in the guide.
Good luck!