Upper Warlingham was indeed closed after this train left, and reopened shortly afterwards, when daylight became sufficient.
There’s no easy way out of this one at UWL - once you open the doors, you’ve got to dispatch the train, and unfortunately this is one of the worst platforms for visibility on a 12 coach service, with a steep curve. So the driver would have no choice but to walk down.
DOO bodyside cameras do have a minimum light level required, which is why station lighting upgrades are regularly required before bodyside cameras are used, and subsequent trains can’t call if the station has been reported to be in darkness. For the avoidance of doubt, it would not be much easier for a guard at this location, as they too would have to walk up and down to see the train clearly in the dark (many of the stations in this area have limited ambient lighting), although it wouldn’t take so long.