This is only natural especially considering their status as refugees. As someone who’s been displaced myself, I cannot emphasize enough what a traumatic experience it is. People in such a situation, finding themselves in a foreign environment and feeling alone, tend to insist on banding together with others of their same nationality and circumstance, in a way people might describe as “exclusive” or “insular”.
I agree with another poster that your priest is too be applauded for the welcome he’s given this community. Please try to understand yourself that there is nothing wrong per se with the “mixed” host issue (I place it in between quotations in order to demonstrate how silly it is to discriminate between hosts) and the banding-together issue.