You’d already know this if you subscribed to Hop Queries, my free monthly newsletter. From the October issue:
I have a new favorite answer to the question about why dry hopping is called dry hopping. The idea came up during a panel discussion at the Craft Brewers Conference earlier this year, but John Paul Maye of Hopsteiner crystalized it during a presentation at the recently concluded World Brewing Congress.
He pointed out that brewers in England had noticed that dry hopping beers ignited refermentation even before Brown and Morris published “On certain functions of hops used in the dry-hopping of beers” in 1893. Because refermentation lowered the final gravity the beers finished dryer, it lead some of them to begin calling the process “dry hopping.”