I also have a memory of the vendor telling me that they're running out of food. Not in the "what do you have to trade" dialogue option, but if you ask him about the situation between the druids and tieflings.

The food in the crates: eh I would separate this from the internal logic of the world. The food is in those crates because Larian put it there for the player, but this doesn't necessarily mean that the NPCs are aware of it. Also, "will run out of food" is not the same as "already out of food."

That said, it is incredibly silly that druids would run out of food. They can cast goodberry, feeding 10 people per day for the cost of a single sprig of mistletoe. They should also know how to live off the land. And, if they're running out of food now, how does it help them to "close themselves off from the world"? Won't they just run out of food even faster without the ability to forage/hunt??