The film is in the same universe as The Truman Show
Luther and Nora are unknowingly the stars less successful show from a rival studio that tried to up the ante by having two real people — a husband and wife — amidst the actors instead of just one. The events are all how the studio is forced to railroad the couple into following their script when they unexpectedly decide not to celebrate Christmas. Obviously this would be terrible news for the television channel and their donors, who want to advertise Christmas products used by the Krank family. That's why the whole neighborhood conspires to guilt the couple into celebrating a traditional Christmas, culminating in the return of their daughter — more likely an actress paid to pretend she's their daughter — returning from abroad with a husband; obviously a contrived last-second rewrite intended to guilt the couple into going along with the Christmas celebrations. Alternative, it's an in-universe a movie made for Truman
The movie had the moral "you should do everything your neighbors tell you, instead of going abroad with your wife and having a nice cruise. Doing that makes you a dick." This movie is legendarily stupid, and not just because of how insane the message is. But it's the exact movie that Christof would make Truman watch. In one scene, Truman is watching Hallmark-style movies that preaches the same moral of staying true to your town. Throughout Truman's life, he's been fed this nonsense to keep him in town. And considering the crap real Hollywood makes, there would be no shortage of similar slop that Truman Show can buy. Maybe they have screenwriters on staff who churn out this material, and then go on to sell these movies to other studios. Maybe Nielsen secretly tracks Truman's reaction to movies, and film university students study these reactions while learning about how not to make mediocre art.