I know this is ridiculous, but it seems to me that The hole in the tree could be where the 5 villagers came out to this new part of the island. The villagers are all in the same area, so maybe they just newly came out of the hole. I mean, the tree could be magical or connected in some sort of a cave.

MAYBE they were banished by the tribal chief for practicing forbidden magic. (basing on the previews page picture, hehe.)

If you look at the Isola picture in Plant Tycoon, there is a big possibility that there will be a beach in VV4.