I am not an expert in everything, so I have no ego to check when to comes to subjects that are outside my realm of understanding.
The behavior of concrete in commercial buildings (like the WTC) when subjected to intense heat is one of those subjects that, amazingly, I am outside of my expertise.
The caption provided in the NYPD Museum that seems to speak to this, would need to have some science behind it in order for me to take it as written.
Otherwise, I'd have to conclude that they're just pulling it out of their proverbial asses.