1) What happened
Wrong lightmapping the terrain
On using different lights in scene weird squares appears on the terrain

2) How can we reproduce it using the example you attached
1 Open attached project
2 Open scene "1"
3 You should see squares on the terrain (like on attached image) which appears after Lightmapping
To check this:
Open Window->Lightmapping then choose "Bake"-tab and press Clear (the terrain should be without squares )
Then press "Bake Scene" and after baking process - squares again