One of his mates Brodie Ellison posted: "Bloody proud of you mate, well done. Next time no fish products to be consumed all week. Now hit the range!"
Campbell replied: "That's a deal mate haha."
The former World No 6 amateur had an up-and-down final round. He started nervously with three straight bogeys but soon got into his work with three birdies to get back to level par after 11 holes.
He traded another birdie and bogey on the back nine before making a double bogey on the 18th. But it didn't matter as he was safely home by one shot.
Campbell was one of only two amateurs to advance from the French event. Former US Amateur Champion Kelly Kraft carded a two-under par final round of 69 to win the European tour qualifying school first stage at Golf d'Hardelot by two shots.
The 23-year-old American will be hoping to follow in the footsteps of his two immediate predecessors to the US amateur throne, 2009 champion Byeong hun An and 2010 winner Peter Uihlein, who have played on the European circuit this year.