They very likely were exposed to the same kind of anti-immigrants propaganda most governments use against their citizens. It happens pretty much everywhere.

Immigrants can't vote, so they're extremely easy to use as scapegoats because they can't fight back politically. Once a government plants in their citizens that immigrants are the root of all evil, they've pretty much won: anything wrong in the country will be attributed to illegal immigrants so that the attention will be taken away from the government. It's the same old trick of blaming a weak minority that cannot defend itself using any legal means, and frankly I find appalling that people still falls for it.