Dear Henk,
About your question: "How does the "Listing Categories block" Content Template get selected/inserted into the view As It Is In The Demo … ?"
Answer:
Views allows Content Templates to be connected to a View. So in this case, the content template named as "Listing Categories Block" is already connected to a "Listing Categories View". You can see this connection by going to the "Layout HTML" and then clicking "Content Template". Then selecting "A Content Template that is already connected to this View". Then you can choose "Listing Categories Block" and add it/insert to the layout.
Usually to add an existing Content Templates to the View and have it inserted to the View, you need to click "Content Template" (in the Layouts HTML) –> and then in the "Add New Content Template. Select "Connect an Existing Content Template to this View" (see screenshot2.jpg). And then select from the list of Content Templates available. You cannot anymore connect templates that is already connected to the View.
This is the new method of inserting Content Templates in View. Please let me know if you have follow up questions relating to this 
Thanks.
Cheers,
Emerson