Regardless of the confusion, something whether rebar or cables allowed the lower structure of the concrete bridge to be moved to be placed on the piers. I suspect we understand the lower part of the bridge below what would have been the neutral axis cannot be allowed to be subjected to a tensile load. I believe that something happened after the bridge was in place that created a tensile loading leading to the collapse.
.
The dead load of the structure itself created a large tensile element.
That is why there should have been falsework in place until the cables took up the load.