Annabel's memory is playing serious tricks on her. For a start, the driver didn't take off his jacket or even do any kind of business in the car boot/trunk. Secondly the red van in question parks beside the car Annabel is in; it doesn't drive off at all.
The joke was that Annabel was being driven somewhere in a private car. The first part of the jokes was that the driver parks beside a brick wall, and then temporarily leaves the car leaving Annabel still inside reading a newspaper. At that moment the red van comes along and parks beside the private car, trapping Annabel inside. Red van driver walks off, driver of private car returns and goes off to find driver of red van.
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