User blog comment:Argorrath/Treyarch posts a message of zombies; possibly hinting to a DLC 4/@comment-184.5.98.212-20130731223812/@comment-356904-20130731224352

It doesn't have to be anything. This could be fluff, or it could be a red herring. Either way there's not any proof that it is definitely going to take place within the 1914-1918 timeframe.