I don't really care but I would consider "Christmas" as a genre to mean that Christmas plays a crucial role to the plot of the film. There are some obvious ones: Elf, Christmas Carol, A Wonderful Life etc, but others cross genres... Love Actually is a romance/Christmas film because of all the gift-giving, the Xmas #1 plot, the nativity, etc, Home Alone is an action/Christmas film because of the family vacationing for Christmas, the house being decked out, decorations being used as booby traps etc... but in Die Hard, the fact it happens to be Christmas is pretty immaterial to the whole thing.
But like I said, I don't care
I just consider it an "action" film and that's it.