Richard Curtis may be a rom-com staple auteur, but that doesn’t mean the writer/director thinks all his films belong on the nice list. Curtis, who makes his animated film debut with “That Christmas,” told IndieWire that another of his anthology Christmas films actually set the stage for his Netflix children’s feature: “Love Actually.”

While Curtis co-adapted “That Christmas” with Peter Souter from his own bestselling book series, it’s Simon Otto (“How to Train Your Dragon”) who directs (“I’m very much not number one here”); for “Love Actually,” Curtis pulled double duty back in 2003. Both films center on an ensemble cast with holiday-centric stories intersecting between characters. As Curtis told IndieWire, it was the “catastrophe” of editing “Love Actually” that helped bring “That Christmas” to the screen.

“The strange thing about ‘Love Actually’ is, when we finished the movie, it was a catastrophe,” Curtis said of...