Did they say why they need to do it this way?

Is there something special about the ground that needs a continuous pour?

Also:Also:

“Vertical construction started the following day,” he adds.

I would think it would need to set and cool first

Example:
https://en.wikipedia.org/wiki/Hoover_Dam#Concrete

Bureau of Reclamation engineers calculated that if the dam were to be built in a single continuous pour, the concrete would take 125 years to cool, and the resulting stresses would cause the dam to crack and crumble. Instead