I haven't found any information indicating that he told this particular story. There could be a misunderstanding or misinformation. Maybe it was someone else who was supposed to tell the story, or the story might not even be related to John G Paton at all.
The story 'A Drink in the Passage' by Alan Paton is likely to explore themes such as race relations. It may show the experiences and interactions of different races through the setting of having a drink in a passage. The characters might face various forms of discrimination or acceptance, which are common topics in Paton's works.
Another important theme is morality. Many of his characters face moral dilemmas, like in 'The Moment Before the Gun Went Off' where the main character has to deal with the consequences of his actions both morally and socially. His stories also touch on the theme of social justice. He shows the inequalities in society and how people are affected by them. For example, in 'Cry, the Beloved Country', we see the poverty and lack of opportunities for the black population, and how this is a result of the unjust social system.
Jill Paton Walsh's fantastic fiction often features richly detailed worlds. Her works might have complex characters with deep backstories. For example, in some of her stories, she creates settings that are both magical and yet relatable, like a small village with a hidden magical realm.
First, look at the racial themes. In 'Cry, the Beloved Country', the relationship between black and white South Africans is a central theme. The novel shows the disparities and the need for understanding between the races.
The drink might serve as a plot device to introduce a new element or change the dynamics between characters. It could also represent a form of comfort or escape in the story.
I'm not entirely sure without re - reading the story, but it likely includes characters from different racial backgrounds, perhaps a black character and a white character, who are brought together in the situation of having a drink in the passage.
There is also 'Gaffer Samson's Luck'. It has a really interesting plot full of elements that are typical of her style in fantastic fiction. In this work, she creates a world that is both familiar and strange at the same time, and the characters are very engaging.