the simplest solution would be that Russell, after wavering for several months about whether this was truly a big one ( "The Great War"), finally decided he had hit the jackpot and published a proclamation accordingly, figuring like Publications Clearing House "You may already have won!"
Wasn't this idea (that Satan was cast out of heaven in 1914) only invented in the 1920s? After all, the Bible Students foretold Armageddon for 1914, not a war, and later they claimed that instead of "early October 1914" it would be "soon after 1914".
The statement "We were right with 1914 but wrong about what would happen" was made later AFAIK.