What details do you notice that show this story is not taking place in the United States? Is Ravi’s experience unique to his culture?

"Games at Twilight" is the first story in Anita Desai's collection of short stories, Games at Twilight and Other Stories, originally published in 1978. "Games at Twilight" is the story of Ravi. As a reader, we feel closer and closer to the young boy as the story shifts from third- to first-person. Early on, there are hints that this story takes place outside of the United States; it's a hot day, and all the children are kept indoors to stay out of the sun. While this may be custom in some parts of the Unites States, perhaps in the South, it is not too common.
The setting of the story continues to unfold. Raghu is Ravi's older brother, and the person Ravi looks up to the most. He is the "seeker" in their childhood game. The children all run to hide, and Ravi realizes his choices for hiding places are limited. His brother Raghu has what are described as "long, hefty, footballer legs," meaning it is unlikely Ravi could outrun him. "Footballer" is not a word used in the U.S., and its use in this description is likely a reference to how common football, known in America as "soccer," is in India.
In another quote, the narrator describes a neighbor. Once again, some of the language choices indicate that the speaker is not in the U.S.:

… moaned the grandparents who lived alone in their spotless house with a black Labrador who had made a habit of visiting the Ramans whenever he wanted young company, a romp on the lawn or an illicit biscuit.

The phrases "romp on the lawn" and "biscuit" all stem from colonial British influence on India. In addition, Rhagu, Ravi, and Raman all are common names in India.
In another story in the collection, "The Farewell Party," a family is throwing a party to say goodbye to their close friends. Here, there is another clue that the stories are set outside of the U.S. At the very end of the story, one of the attendees sings "Tagore songs." This is a reference to the Begali artist and poet, Rabindranath Tagore. The narrator says of the singer:

... the eyes of her listeners, sitting tensely in that glassy, inky dark, glazed with tears that were compounded equally of drink, relief and regret ...

The cultural references throughout the stories highlight the setting. The work of Rabindranath Tagore is not commonly known or referenced in the U.S. However, it is common in India. Thus, it makes sense that, at a celebration, his work would be sung.
However, it is important to note that Desai purposely makes her writing universal. While it is made clear that the stories are set in India, the ultimate message is about childhood. The main character is experiencing feelings of isolation, freedom, and fear. Desai is exploring the psychology of a young child and the power of his imagination. These themes are universal across all cultures.
For example, the quote about the Ramans referenced above is familiar to American audiences as well. A neighborhood black Labrador is a relatable familial scene in American culture. In addition, the feelings of unworthiness and the need to impress are present among all children. Ravi does not think of himself as an Indian child; he is simply a child, and he is preoccupied with winning his childhood game and impressing his older brother.
In their review of Desai's work, The New York Times stated, "sometimes a mango is just a mango." The Times frequently critiques many works about India and the overindulgence in representing a stereotypical Indian culture. Conversely, they say of Desai's work:

Whether in India, Mexico or America, Desai’s characters tend to be easy marks for new possibilities — for something, anything, other than life as it is.

Here, The New York Times agrees that, while her stories may be set in India, they are designed for every reader to relate to.