For the sake of clarity, I include The Theory Book’s p.253 definition:
Propaganda, n. 1. any organization or movement working for the propagation of particular ideas, doctrines, practices, etc. 2. the ideas, doctrines, practices, etc. spread in this way. (Webster's New Twentieth Century Dictionary)
Propaganda: 3. a storyforming/storytelling technique used to impact an audience in specific ways, often employed to instigate deliberation and/or action. (Dramatica)
It’s pretty much the same thing. For Dramatica, the story becomes the vehicle through which a message is being sent.
The manner in which an author propagandises a story would be of the kind described above - which is to deliberately leave out a pattern or patterns in order to force the audience to fill in the blanks.
The reason the missing patterns need to be hidden is so that the audience doesn’t suss it out. The missing patterns can be made to be quite obvious, but then the audience has a choice in whether to accept the message or not. (Choice, oh no! Can’t have that! Lol!)