As you noticed, steel work goes up FAST, and in this building theres no concrete core, so everything is steel. I'm guessing they still have to pour the concrete floor slabs, but maybe that will happen as the same time as the curtain wall.
I know when they were working on the lower half of the FMC tower it looked like 2 gangs of steel workers could blow thru about 4 floors a day. Just like me and my elector set many years ago.