The "flapping fins" and "two great mugs thrust out from each side" certainly seem like ailerons and ballast. And the mentions of it going at "a great rate of speed" sound like what happens to dirigibles when they get caught broadside in side drafts. What's interesting is the mention of a metal prow. Later dirigibles had docking tips and lightning rods on their noses, but a metal prow seems like it would cause a lot of issues with center of lift. My only guess is it was some kind of lifting surface and the entire craft was an aerostat and not a true lighter-than-air craft.