I don't think it's a cultural thing - some people just decide to stay outsiders, and a subset of those people are rude by anyone's standards.
When I was in grad school, the Chinese students formed their own secret society to the extent that non-Chinese might never even know their name. Indians also had a secret society, but unlike most of the Chinese, they individually interacted with the outside world. Israelis, Russians, Koreans and various flavors of African all integrated more or less completely with the outside world.
In concrete terms, Chinese math students joined the Chinese soccer team and had Chinese advisers. Indians had secret Indian parties, but they played on the Math soccer team. Russians invited people of every nationality to the Russian vodka drinking parties.
Yes, but Russians have been using the ploy of "getting the foreigners drunk" for centuries! This has been a key element of their government's diplomatic strategy forever, and I hear that it's often used in business.
Similarly, where I went for undergrad, Koreans tended to have their own groups. Clearly they don't do that everywhere, and not all of them did - there were just enough of them that didn't want to integrate that it was easier for others to choose not to. A segment of any group does it if they're a large enough minority - it wouldn't be fair to criticize one particular culture for it.