For being detained for 4 days, though? It seems reasonable to me for mistakenly arresting him. It doesn't excuse what sounds like unkind and rude behavior from the officers, though, which they shouldn't be doing even when really deporting someone.

4 days of mental anguish and distress is worth more than that. It's a stress and pain that will stay with a person for a long time. It also has to be enough of a deterrent so that the agency is more careful next time.

Sounds extremely low. They violated his rights.