I'd also point out, no one is demanding to see your immigration papers prior to an administration coming along and acting like citizens have some god-given duty to root immigrants out of their communities. Lots of good laws exist that for also very good reasons we don't enforce that strenuously. The culture of how hard we look for rule breakers is just as important as what the laws are themselves, and creating this cultural panic and atmosphere of paranoia where a guy feels the need to check out his pizza delivery guy is just as damaging a consequence of Trump as any actual policy change. This sort of shit doesn't happen otherwise.
But this wasn't a "show me your papers" case.
No one's getting on a DOD installation without proper authorization. Usually that's a DOD ID card. Or it's a visitor pass, granted after the applicant clears security.
In this case, the database that the Army uses reflected an active federal removal order — I don't know the applicable AR here, but I'm analogizing from my Air Force days under what circumstance we'd notify DoJ for, say, an outstanding bench warrant for failure to pay child support.
It's very likely that Army policy was to notify the cognizant federal agency (ICE) when faced with knowledge of the removal order.
I'm sympathetic to the driver, but I'm more surprised that it took this long for him to get arrested: how did the database NOT reflect the removal order until now? You aren't getting on post without a pass; it's odd to me.