I really, really hate to admit it but I share your feeling, jura2.
I am not aware of any statistics, but I just have this feeling that many non-EU migrants resented the EU migrants' right to freedom of movement, forgetting that it was mutual. We could travel to other countries in Europe, work or study there or retire there - in a way we are not free to settle in third countries from which some migrants are descended.
This is all the sadder - to me at any rate - because the majority of migrants here are non-EU migrants who have come to this country for a much longer period of time. Whatever other reasons they might have - quite legitimate - for supporting Leave, I can't help feeling that for some there was an element of resentment.
Of course, that is not true of all non-EU migrants and maybe even generalising is dangerous.