After reading Taylor Marshall's account of the 1914 Conclave, I have come to the conclusion that the election of this Pope is in fact legal. My previous speculation that he may be anti-pope was based on the mistaken idea that his election was Not in fact legal.
Marshall also discloses that while the Pope did dissolve the Sodalatium Pianum, he left in place the ex-communications of Modernists pronounced by Pius X.