I was 'not' arrested by DHS/CBP.

They simply got a warrant retroactively after they already did it. Released without charge, but they just invented some paperwork afterwards that an anonymous dog had alerted (judge signed it about 12 hours after I was 'not' arrested). No mention on the PC paperwork who the dog was or who the handler was, as far as I know they didn't exist.

So yeah that's nice in theory but in practice they can simply jail you without recording an arrest, then retroactively invent PC. When I ran a federal background check it came up with no arrests, despite the fact I was imprisoned.