Unintentionally being exclusive

I asked my daughter for her first impressions or general impressions of Chinese students, her impressions were generally positive, and she  can always find positive things to say about specific students. However, when they are grouped together, or in a group setsetting, an invisible barrier automatically forms. It may not be their intention to keep outsiders out, but it sure appears like that to outsiders. My daughter tried a few times to join the club,  she finally gave up. It is the subtle things.