I don't like the term, mainly because it panders to the idea that excessive drinking can't be "cured".
My interpretation is that for someone who spent many hours of their life drinking, they've developed routines to fill the 24 hours that make up a day. When they stop, all their "drunk time" is suddenly free, and they sit around wondering what to do - which for me was a recipe to start drinking. Once the not-drinking-routine becomes the norm, the "dry drunk" is just a normal person again.