The upper floor columns do look too slim to be carrying the weight of the roof but the structural load should have been calculated by the engineer.. From this angle, we cannot tell how much structural support there was in the center of the building at the roof.
What is telling is that the lower structure started collapsing at the same time as the upper so it wasn't pancake effect of the weight of the roof collapsing each floor below it as it fell.
Concrete usually takes 28 days to cure, and this building appears to have had all the formwork or shuttering removed, which shows that concrete should be near full strength.
The facade usually hangs off of this structure, so it generally does not offer more structural support. So that shouldn't necessarily have been a factor.
Often in earthquakes, the building starts to rotate and this causes the columns to crumble and lose any stability.
In my province, here in Canada, any emergency building, such as hospitals have to have added structural integrity to withstand an earthquake.
On one building we ran steel cables from the roof, down 85 feet into bedrock then put 1 million pounds of tension on the cables to hold the building in place so it wouldn't rotate if struck by an earthquake.
Some buildings like our CN tower are built to sway 6 feet or more and not be too rigid.
Amongst all the other scenarios possible, it would have been terrifying to be in a rooftop infinity pool when all the rocky and swaying began.