Last week I was checking in for FRA->IAD when I encountered an extra officer at the entrance to the check in area (all lanes). They started to ask me question. Not the standard "have your bags been with you, etc." type of stuff but they went fairly deeply into "where are you coming from? what did you do there? how long did you stay?" which tend to be more CBP like question. I wasn't in the mood for it, so I started pushing back. It went something like this:

Me: "If you don't mind me asking: who are you and why are you asking me these questions?'
Them: "We work with the TSA"
Me: "So are you an employee of the Department of Homeland Security?"
Them: "We are helping out with safety" (or some other non-committal nonsense)
Me: "Are you an employee of the Department of Homeland Security?"
Them: "Well, yes, we work with them"
Me: "So you are an actual an employee of the Department of Homeland Security?"
Them: "Well, no, but we are working for them, have a nice flight"

At that point they waived me through, clearly uncomfortable with my line of questioning. I fly US<->Europe fairly frequently but the only other time I've encountered this was maybe two years ago in Brussels. At that time I was too surprised to push back, but it did prepare me for last week's interaction.

What the heck is this all about? Has anyone else encountered that recently? It seems weird and also somewhat futile: After all, I was able to push my way through them without actually answering any of the questions that they were trying to ask.