I'm sending this postcard to a friend (who used to live in HK and knows that the city is nowhere near the Great Wall of China) as a joke, and am hoping that it doesn't further any pre-existing geographical ignorance among those who might see it.
So, I wonder why they produce and sell this postcard in Hong Kong. Admittedly, it's pretty hard to find here -- I've only ever seen these at the Temple Street night market -- so was it an accident? Has it been reprinted as a joke?
Any other hypotheses?