How had Jim been captured?

A boy explains that a man recognized Jim as a runaway from a handbill that offered $200 for Jim’s capture in New Orleans—the same fraudulent handbill that the duke had printed earlier. The boy says that the man who captured Jim had to leave suddenly and sold his interest in the captured runaway for forty dollars to a farmer named Silas Phelps. Based on the boy’s description, Huck realizes that it was the dauphin himself who captured and quickly sold Jim.