... the strop is WAY to short ...
Normally I would agree, but in this case, they are using that hook that can swivel the load around to align it correctly on the roof, without having to use lines with people pulling the load to the correct position. They have 4 lines on the unit and making them too long, would probably twist them.
I think they knew what they were doing, regarding the rigging ... until the moment all went wrong, but I don't think the length of the strop is the problem.