Carl's throwaway movie quote is the clue that led the liaisons to his hidden residual conversation.
When Carl asks how they figured it out, Orren has to recall the exact words before answering: welcome to the party, pals. He tells Carl that never before has a single sentence caused so much fear amongst his team.
From that thread the Liaisons worked backward and finally recovered the concealed conversation between Carl and the Residuals only a few hours earlier. The consequence was immediate: Harbinger sent an order to have Carl killed, and The AI intervened on Carl's behalf. Carl's reaction is rueful — he knew he should have kept his mouth shut.
The offhand quote that betrayed Carl's secret and nearly got him assassinated.