After arresting Chad, Booth and Bones stop to pick up baby wipes and diapers. When they're done, you can see that Chad isn't handcuffed. He's actually holding the cuffs in his hands.
Finn says that the victim weighed 122 pounds, which Shaw says was the weight difference between the truck when it crossed the scale and when it pulled in to the weigh station. However, Bones later pulls Barb's head out from under the truck, accounting for at least a few pounds of weight that was still on the truck.