From the article:
When we went to our seats, the wait staff let us know that despite the fact that the previews were playing, we wouldn’t know until the movie actually started whether we could see the film or not. If it didn’t work, the screen would just turn black. Luckily, the film went through without a hitch.
80% certain it's DRM to stop theatre owners from pirating it between each other and not to stop the public from having those copies
Come to think of it there's probably something to make sure theaters are completing the number of contractually obligated screenings too. Like a 3 person screening is probably a loss for the theater, but not revenue distributers want to lose out on.
Yes, the amount of showings that a theater has is tracked. Certain movies are contractually obligated to show at certain times or a certain number of times a day.