I believe that the issue isn't high and low trust countries but rather that people in the general case trust others who are like them, because they feel shared interests. I've read some studies that the more multi-cultural a society, especially if there isn't a shared concept of a nation in the immigrants, there is less trust because people do not view their peers across cultural lines as having their own interests. Basically multi-cultural societies in which there isn't integration, shared values, etc. lead to low trust as each group views them as competing with the "different" others.

Even if all the groups came from high trust countries, if combined they do not feel a sense of shared values, patriotism, they will have low trust between these groups.