I always thought that either the fresh berries were from someone sneaking in and getting them from the bush, there was another berry bush somewhere else on the island, or that there was another GC like character who can magically create food.
He or she would have to be GC-like in order to move the boulder back and forth (as I can't figure out how they'd sneak in to get the berries from the bush without moving the boulder) or to magically create food. A slightly frightening possibility.
