Continuity mistake: In the scene where the van crashes into the dock's factory doors, the van is stood there in the factory. But when it cuts to outside of the factory, the van is on the road, and no-one drove it there.
Continuity mistake: When Scooby, Daphne, Mary-Jane and Shaggy are being chased by monsters and crash through a window off the luggage cart, the window is already broken before they make impact on it. (00:42:30)
Answer: It's never explained. We're just left to assume he was somehow able to.