Looks like environment lighting to me. I'm not sure this is the case in your example, but a lot of render engines use an environment light when rays don't dete

Looks like environment lighting to me. I'm not sure this is the case in your example, but a lot of render engines use an environment light when rays don't detect collision. So the camera is looking at the wall of the house and bounces into oblivion. Therefore the environment values are used. And since the stones of the house are gray a lot of environment light bounces back to the camera. But when the camera is looking at the trees a lot of rays bounce to leaves and the ground returning almost no light back to the camera. I would even say that your example looks realistic (although way to dark).