Instead of citizens, we would say People who are legally authorized to remain in the United States? Is there a word for that?

Technically not a word, but the US government uses "lawfully present individuals" in its policy docs. In addition to US citizens, this covers lawful permanent residents, people with valid non-immigrant visas/visa waivers, some country-specific exceptions (e.g. Canadian citizens visiting for short-term business and pleasure), and various humanitarian categories (refugees, people seeking asylum who have filed the proper paperwork, etc).

In short, an unfortunately very wide field of people for ICE to chew through without touching any citizens (even if one takes the most uncharitable interpretation, i.e. only 70% of arrests have been of unlawfully present individuals)

I had misremembered the claim as "70% of the people ICE arrests are criminals". The inverse of criminal cannot be someone here illegally.

Doesn't matter. I made a claim without double checking something I should have, or adding nuance or fleshing out my claim. I made a false claim.