Near the end of the movie when the bad guy gets killed and his spirit is leaving, his body is in the street next to the car that hit him. Then, when his spirit looks back, the body is on the car hood.
Watch the movie carefully, and you see what happened. Willy is hit by the car, and the impact knocks his soul out of his body. His body is left sprawled on the car. His ghost, laying on the ground, is stunned for a moment, then gets up, walks to the car, then looks in horror at his own body. Then, Sam mocks him, telling him he's dead, then the dark spirits come to take Willy to hell.
I was also confused by this at first, but it's not a slip-up. When Willy gets crushed between the two cars, his spirit is what goes flying through the air, landing on the ground. When he wakes up it is his spirit that looks over to find his physical body laying across the hood of the car. That's when he realizes he is dead.