I was just working with a John Cage recording on in the background which included his reading of excerpts from his journals. It included Cage telling this story, and it made me want to see what "going out of Holland backwards" meant, so I Googled it.
I still don't know what it means, but when Cage told the story, he was the smoker, and instead of "wife," he said "Merce Cunningham":
In 1959 my wife and I toured Northern France and the Low Countries by traveling the intricate inland waterways – the canals that pervade this part of Europe. As we were leaving Belgium and entering The Netherlands, the fog became so thick that instead of our barge docking at a customs station, to expedite matters, customs officials came aboard the barge.Non Sequitars [sp] [rememory.com]The passengers formed into several lines, and one by one were questioned. My wife was in one line and I in another. My wife was a smoker and I was not. However, I was taking five cartons of cigarettes into Northern Europe for her, and she had that number herself.
We were traveling through Holland to Luxembourg, and back through Belgium to France. The customs of all those countries varied with regard to cigarettes, For instance, you could at that time take five cartons per person into Belgium, but only two per person into Holland.
When I got to my customs officer, all of this was clear to both of us. Out of the goodness of his heart, he was reluctant to deprive me of my three extra cartons or to charge the heavy duty on them, but he found it difficult to find an excuse for letting me off.
Finally, he said, “Are you going to go out of Holland backwards?”
I said, “Yes.”
He was overjoyed. Then he said, “You can keep all the cigarettes. Have a good trip.”
I left the line and noticed that my wife had just reached her customs officer and was having some trouble about the extra cartons. So I went over and told the officer that my wife was going out of Holland backwards. He was delighted, saying, “Oh, in that case there’s no problem at all.”
John Cage Featured on KPFA's Ode To Gravity Series (December 12, 1987) [archive.org]