The turning point in their friendship was when they come to the city.
Before that they were living in the village his grandmother would go with him to the school since the school was attached to a temple.
But in the city writer goes to a English school and his grandmother does not come with him to his.
Before the writer was taught about Scriptures and his grandmother helped him in his lessons. But not now because the writer was now taught about gravity and Archimedes so grandmother was unable to help him in his lessons and his grandmother disliked it.
So all these came to be as turning point.