That's my guess, also seems odd that the Father would go right to that specific trunk and open it long after the police searched the car. Also I find it odd that a canine capable of smelling even minute traces of anything it's scented on, didn't fixate on this trunk to begin with.
The police never searched that car.
Can you imagine being stopped for a crime, and the police never trying to search your trunk?
And dogs are not infallible. They make mistakes every day.