mmurray - You are correct - and I had forgotten about the Geoscience bathymetric survey, carried out prior to Fugro commencing operations with the towfish.
About all that I could imagine that has happened, is there has been an error in use of the towfish, and/or a miscalculation of the height of the mud volcano - or perhaps they just plain "forgot" it was there!
Seems like someone screwed up - big-time. If the Fugro crew had the Geoscience "3-dimension, detailed, high-resolution" survey to hand - as they should have had - then possibly, some highly embarrassing explanations may end up being produced by the crew, as to how they managed to hit the volcano.
MH370 - bathymetric survey