Earlier quoted context omitted.
Illegal immigrants in the US are most certainly a minority group. It's not hyperbolic and unproductive, it's the plain truth, just like the Japanese concentration camps during WW2.
Illegal immigrants are not at all entirely of a single minority group. And even though they are mostly of a single minority group, that fact is incidental to the fact that they are being put in detention facilities, it is not causal .
How certain are you that Canadian refugees (for example) in equivalent numbers would be subjected to similar treatment and held in similar conditions?