When Lt Marino plays the tape recording of Seth's account of his kidnap for the FBI agents, the wording in the recording is not the same as what Seth is heard saying to Lt Marino earlier.
LT Marino's seat belt while him and Jessica are in the car, goes from buckled to unbuckled while driving.
As Jessica is getting into the car Seth walks out and hollers, "That's the wrong car!" He has not seen the car nor the agents who are supposed to pick them up so he cannot possibly know it is the wrong car.
He knows it is the wrong car because he recognizes the mobsters that worked for Abruzzi.
When Jessica is talking to the police detective in the car he asks if Seth comes to New York often. Even though they are in Boston.