It doesn't sound like he actually tried to pursue that. He was told, "You can leave, but the bag stays." He chose to stay. They decided to keep questioning him.
It's total bullshit. If they found bomb residue on the guy and thought he had a bomb, or like say was checking a fucking bomb through security, they would search the bag ASAP with their dozens of TSA people, instead of just letting a potential bomb chillax in the airport terminal while they try for hours to get some guy to trip up on his answers to questions after he's tested positive for BOMBS. They had obviously searched the bag of course and were just making up some shit to trick him into agreeing to stay.