inspections in airport?

While walking out of MIA, I was stopped by plainclothes law enforcement at baggage claim (I was just walking by with a carryon suitcase, hadn't checked bags). The guy flashed his badge but very quickly so I couldn't read whether it was police or another agency. He asked me custom-type of questions such as where I'm coming from, how long my trip was, any declarations, and where I'm staying.

I've never gotten stopped in that way at a US airport before and was just curious if that's common at MIA? Or perhaps there was a special situation and I fit the bill appearance-wise? It took just a minute so no big deal but was just curious if others had experienced something similar.