It might also interest the Christian world, that our Jewish friend have thought in their literature that Christian are gentiles or goyim.
So what is your point?
In my personal opinion, the practice of calling non-mormons (including Jews)"gentiles" may have started because the early LDS made much of their church being different, or "peculiar". They did NOT want to be seen as just another Christian church, and the "gentile" label illustrated the difference. In my time as a mormon, there was quite a distinction made, and much pride taken it it.