Given Samsung’s flip phone has an IP rating of IPX8, which means it’s protected against being submerged in water but isn’t protected against dust (for now), it seems likely the flour played a part in the phone breaking. But being able to survive 400,000 folds would still mean the phone should survive over 10 years of use if you unfold and fold it around 100 times a day.
Honestly I'm impressed it survived for as long as it did. I played around with a demo model last month, and I figured it'd break rather quickly even with normal use. But I guess the conclusion is as long as you take care of it, it'll be fine. Still think it's all a gimmick though.