Just read that on TMZ. It also mentions engine sputtering before the crash, which means they lost power (lift).
And if it was very cloudy outside, it would have made it difficult for him to find a place to land
What I read said same but also said that the helicopter suddenly rose in height, so power loss might not be the case. Foggy conditions were also reported - possibly flying at low altitude and attempted to raise height abruptly when the hills were noticed. Quite possible if you look at the pictures of the crash site.