Without being able to review the building plans, the materials specs the building's contractors scope and timetable chart, the building inspectors sign off sheets there is hardly any way yo speculate why this occurred. but I do know this somewhere there is an engineering consultant a senior engineer several assistant engineers, a building inspector a project planner and a host of others who's bowels are in lock down mode trying to figure out what went wrong and how to keep their jobs and maybe worried about fines and jail time. Something like this does not happen as the result of 1 persons' negligence.
There were times during the construction of the 829.8-metre-tall Burj Khalifa in Dubai that the accelerated time tables of construction had to be amended due to the cure rates of the concrete not preforming as calculated other times the schedule was able to be the speeded up slightly as well.