So for a reason besides racism/xenophobia...

Lots of immigrants don't assimilate into the society they move into. Most are perfectly fine people who want nothing more than a better life for themselves and their family. But there are also some who don't follow the laws or adopt the customs of their host nation, and they can be very difficult, or outright hostile to interact with.

I can understand someone meeting a lot of people who are like that, and having negative feelings towards that group as a whole. In the heat of the moment and a fit of anger I've felt that way after a series of negative interactions with people who were all immigrants from the same area, and those people were the same ethnicity as me. It's not right, but I can understand.