The berries were already growing there in abundance in any direction on the island for anyone that showed up.
There was nothing special about the 3 guys finding berries.
There was no specific intervention of God for the 3 guys.
Now, if there had been no berries on the island, and God rained some down from heaven (as he did with the manna and quail), then you could say that God intervened to feed the guys.
As the story stands, there is nothing to suggest an intervention happened from God to produce berries then and there for the guys.
The berries were already there for anyone that showed up.
There was absolutely no advantage given in order for any of the 3 guys to find berries on the island to eat.