I learned about the fact this dishes is originated from French dish. It was surprising. I thought the dish was a long traditiional vietnamese dish.
If I tell you more, since Vietnam had been colonized by France for a about 60 years, French cultural traces are present in this asian country, one of which is the rice noodle.
Indeed, vietnamese people created the fusion dish by adding their rice noodle into leftover french soup called in french language "pot-au-feu", which means "pot on the fire"
It reminds me of 부대찌개, well known korean dish.
I think it's meangless to discuss the origin of a dish. It's present thing that counts !