Good story, except that aluminum doesn't float, and beer bottle caps are made of steel. Aluminum is too weak to hold the pressure.
Nowhere does it say that the caps were floating, they were merely washed down the pipe. And aluminum is also used in beer bottling; in my childhood canned beverages shipped in lined steel cans, most stuff sold was in glass; aluminum cans for carbonated soft drinks didn’t catch on in Michigan until the early 1970s. That was around the same time the bottlers here stopped operating their own systems for deposits on bottles and the cases they came in, replaced by a single gubmint “bottle bill” system.