Perhaps he had “angry eyes”.

Well, the most likely explanation is that he was present in the country unlawfully.

I mean, it's possible that's not the case. There are certainly instances where people who are here on valid visas, or under temporary protected status, or parole, or other lawful statuses are also detained for deportation. But it's less likely. ICE is generally detaining people who are here unlawfully.

The big change with ICE is that they're utterly indifferent to whether the unlawfully present people are criminals or not, or whether there is even the least reason why they should be chosen for deportation over the "worst of the worst" that were formerly being prioritized, or whether any humanitarian considerations are taken into account at all. It's not that they've stopped paying attention altogether to whether people have legal authorization to stay here or not.

They're not being careful about this in the early stages - they'll grab lots of people in these raids, and hold onto them for a bit while they check to see their status before moving on. Which is horrible for citizens and lawful aliens to have to go through for no reason, and perhaps even unlawful. But that's not what someone would describe as "disappearing into the ICE system."

What they're not doing, though, is trying to clog up the actual immigration and deportation system with folks that actually aren't present in the country without legal authorization. Not for any beneficent reason, mind you - it's just in their self-interest to try to keep the wrongful detentions at a low-ish level, because those clog up the courts and use up ICE resources at a time when they're under massive pressure to make the unreasonable quotas being set by TPTB. Trying to hold onto a person who is a citizen, or a non-deportable person with status that can't be revoked, is a very low-reward action for them. When the Administration is targeting someone, that might be a different story - but for the bulk folks that are being detained, ICE does have incentives to make sure that they don't keep actual citizens or non-deportable persons in the system for very long.

So while we do not know, and cannot know, the specifics of the person Last is referring to, the most likely explanation is that he was a student who was here unlawfully - someone who would have been allowed to remain under prior administrative policy if he hadn't been doing anything else wrong, very possibly (or even probably) wasn't doing anything else wrong, but was still here unlawfully.