Far too many Christmas films have nothing to do with Christmas. It's usually just happening in the background (snow, Christmas lights, the occasional song and overuse of red and green).
Home Alone is one of the most famous Christmas films, but it could just as well been during in Thanksgiving. The family just need a holiday excuse to leave the house and practically none of Kevin's traps are Christmas related. I can only think of one off the top of my head, and it's the least creative one (when the crooks step on glass decoration with bare feet). I also think that part of the country (Chicago suburbs?) can be snowy, cold and slippery during Thanksgiving, which aids some of the other traps. Even the neighbour's family conflict could just as well have been solved through a Thanksgiving dinner instead.
Or to take a "modern classic": The Holiday. Super popular among the romcom lovers in my family and friend group and now considered a "must watch" every Christmas (I think it's because Jack Black is so irresistibly sexy). Half the film happens in sunny California and I don't think they even say the word Christmas or show a single piece of Christmas decoration. The other half happens in the snowy English countryside but there is only one Christmassy scene that I can think of.
The only logical conclusion is that if the story happens during Christmas and most people watch the film in the Christmas season, then it's a Christmas film.