Check what I've just found: http://news.google.com/newspapers?nid=1499&dat=19270519&id=86ZQAAAAIBAJ&sjid=nyEEAAAAIBAJ&pg=6957,7334812
It appears that they got the story right, as the captions do not suggest that the "Dummy Monitor" was sent specifically to make the Confederates destroy the "Indianola".