This is the stupid kind of questioning that passes for the dog and pony show that is security when flying on US carriers back to the US from places such as CDG and AMS.
I'm certainly no fan of this idiocy. Sadly, this is not just unique to DL, as I've seen it with NW and AA rather often too when flying from CDG and AMS.
At AMS, the "interogator" wanted a piece of my travel companion but my travel companion was not interested.
My game with these people is to identify them and where they grew up and/or learned English.