Theory:

     He left the room and retired for the night, expecting Iswaran to sulk for a couple of days. But the next morning he was surprised to find the cook as cheerful and talkative as ever.

     From that day on Mahendra, for all his brave talk, went to bed with a certain unease. Every night he peered into the darkness outside through the window next to his bed, trying to make sure that there was no movement of dark shapes in the vicinity. But he could only see a sea of darkness with the twinkling lights of the factory miles away.

     He had always liked to admire the milk-white landscape on full-moon nights. But after hearing Iswaran’s story of the female ghost he avoided looking out of his window altogether when the moon was full.
Explanation:
 
Later, Mahendra left the room, and he went to bed. While thinking about Iswaran, Mahendra had expected that Iswaran would remain quiet for a few days because Mahendra had scolded him. But the following day, Mahendra was surprised to see a cheerful Iswaran, and he spoke to him in a casual way. It shows Iswaran had forgotten what happened the previous night, and he was speaking to his master in a relaxed manner.
 
shutterstock_582916999.jpg
Mahendra thought that Iswaran would remain silent for few days
 
Even though Mahendra bravely spoke about the lack of existence of ghost or spirit in the world, Iswaran's ghost story lingered in his mind. So every night before going to sleep, Mahendra would look out of the window next to his bed to confirm that there was no ghost or movement of any dark shades. But instead of ghosts, Mahendra saw only the dark landscape with the twinkling lights of the factory, which was shining miles away from the living place.

Mahendra was a nature lover, and he liked to see the white coloured landscape during full-moon nights. So during full-moon nights, its brightness hits the landscape, and seemed to be milk-white colour. However, after hearing the story of a ghost woman, Mahendra stopped enjoying the full-moon night and its beauty. So whenever it was a full-moon night, he would remember Iswaran's ghost story.
 
arctic-152720_1280.png
Mahendra liked to enjoy the white coloured landscape on a full-moon night
 
Meanings of the difficult words:
 
S.No
Words
Meanings
1
Sulk Be silent, and bad-tempered out of annoyance or disappointment
2
Cheerful Noticeably happy and optimistic
3
Talkative Fond of or given to talking
4
UneaseAnxiety or discontent
5
VicinityThe area near or surrounding a particular place
6
Landscape A large area of countryside, especially in relation to its appearance
Reference:
National Council of Educational Research and Training (2006). Moments. Iswaran the Storyteller– R.K. Laxman (pp. 12-18). Published at the Publication Division by the Secretary, National Council of Educational Research and Training, Sri Aurobindo Marg, New Delhi.