Low clouds can be even worse than fog.
Fog tends to hang around and is slow to move or clear.
Up in the hills/mountains clouds are a real problem because they can move in fast.
One moment your in clear air and the next you have zero visibility.
Pilot states and control confirms that he is navigating following the roads indicating that at that time he was flying in conditions where he could see the ground.
Flight following means ground monitoring the progress of the flight on radar.
Control states that the plane is too low for flight following meaning that it has dropped below the radar horizon or there is terrain between the plane and the radar.
It would appear that he flew into a cloud/fog and hit the ground.
This is known as controlled flight into terrain.