Amazingly there were no fatalities (other than a dog that was in one of the houses that collapsed). When you watch the video of that accident instinctively everything tells you that it is much more than just material damage, and I clearly remember being extremely relieved that nobody died.
Yeah it was really startling to watch it unfold. It's difficult for me to follow since little technical info has been released in English. What I can gather is that they failed to account for the changing stability of the barge, and coupled with a crane that wasn't designed to slew while tilted shit hit the fan.
I can imagine that a dual crane lift introduces a lot of variables that are not nearly as well understood or tested by manufacturers as the parameters on a single-crane lift.
Here is a video of the accident:
https://www.youtube.com/watch?v=k2Da6FoWh3k