I don't personally believe them to be so, but just for argument's sake.
There are arguments that have been made for this. The book “The Origins of the Second World War,” (Taylor) for example, posits that it is essentially one long war with an intermission. The armistice created conditions that made further conflict inevitable since it essentially forced Germany to take full responsibility for WWI and crippled their industrial capability. He also paints a picture of overzealous allied powers wanting vengeance on Germany to a degree. He positions Germany as striving to get out from underneath the Treaty of Versailles, and it just so happened that Hitler was the one who was able to do it. I have seen similar arguments to the above elsewhere but I am away from home and don’t want to mix up sources.
However, I also believe that this particular book has garnered a good amount of criticism, even at the time. Some felt that Taylor used distortions of history to help “prove” his clever ideas, and that he was more concerned with being clever than right. Others felt that by pointing the finger to various external forces (appeasement, Hitler’s nationalist ambitions being similar to other German politicians, the ToV, etc.), he was taking blame away from Hitler and others and deflecting from the evils brought about via events like the holocaust, among other things.
I suppose it’s up to interpretation. Cases have been made both ways, probably louder (but not necessarily more correct) ones on the side of “one long conflict”. I like the post that Gasmask134 links in this thread that discusses how proximity to events shape our view of their distinctiveness. Perhaps it will merely be a question of time.
This question comes up quite a bit, here are some answers I managed to dig up
This on by u/faceintheblue which brings up the point that since we are still so close to the two world wars in question we aren't comfortable with marking them as the same conflict.
This one by u/Commustar
I will also link this answer by u/AshkenazeeYankee while it doesn't talk about the world wars, it does discuss what people of the 17th century called the Thirty Years War, which goes back to the first answer I linked as people who lived in the 17th century referred to it as multiple conflicts, meanwhile 400 years later we categorize it as a single conflict.