I could be considered an international student (though SFE considers me to be a home student) because I moved from abroad to go to uni. In my flat were two Cypriot twins who never talked to us. They actually used to leave notes on the kitchen table to complain about things rather than talk to us, which I personally just found unbearably rude. Their English was fine, one of them was actually studying English and the other Biochemistry. To get into uni you have to take an English test anyway, so it's actually hard to be bad at English and still manage to take a test (including conversational/oral skills) and do well enough.
They didn't stay in their rooms all the time (when they did it you could tell because they had rooms next to each other and would often speak loudly/shout rather than go into the other person's room, and I was opposite them in the corridor), they often brought people back if they were home or went to their places... all of their friends were Greek.
Seems kind of sad to me to come here and not interact with anybody but those you could speak to at home. Though this is obviously anecdotal and doesn't mean anything, from what I've seen, it's an unfortunately accurate stereotype. It's also really difficult to just go over and start speaking to an international student when they're speaking in their native language with a group of people from their country
It's hard enough to just walk over to a group that seem to already know each other and introduce yourself, let alone when talking to them would mean that they had to speak in your language rather than their own.
That said, keeping an open mind is the best policy. I wouldn't want to have it in my head that all International students are like this, espeically seeing as personally I'd find it really interesting to speak to people from other places and would like to have more International friends.