I sometimes wonder if the park made up that description to lower expectations for the show or to surprise people. Based on concept art that the park posted one season outside the Globe Theatre (which had dates on them originally) the set and projections for the non-rock Scrooge No More were designed at least two years before the announcement that Zachary quoted was given. Both productions might have been in the works at the same time, but I have a sneaking suspicion that the rock version of the show was just a red herring.
That said, a lot of the music in Scrooge No More (especially Just Leave Me Alone) sounds sort of rock-like, so who knows what happened between that announcement and the show’s debut.