I had a customer back then who was a retired Prof of Architecture..He told me he had worked on the construction of the Towers and that the WTC did not have a layer of concrete poured over any of the beams as was SOP until the 70’s in NYC.As a result he had no problem believing that the steel was melted quite quickly
I read a fairly good book on the tower collapse - I wish I could remember the name...but it was ‘just the facts’ and described what had happened, what limitations the building had that hurt, what aspects of the building were good, etc. Lots of stuff about locations of stairwells and stuff like that. But no politics, no finger pointing - just the facts.
It also touched on the fireproofing. One of the towers was built with less fireproofing than the other - and this turned out to be the first one to fall. If you recall, the second one hit fell first - and it could have been because of insufficient fireproofing. Anyway, in the years prior to the attack, the Port Authority had been improving the fireproofing any time a tenant ended their lease. They would gut the empty floor and add fireproofing but they were not finished with this process.
So one tower had good fireproofing, by modern standards, and one had substandard fireproofing.
Now another aspect of this, which might be what the professor was referring to, is that the fireproofing fell off. It isn’t meant to withstand being hit by a collision with an airplane. So the impact of the airliner almost certainly knocked off a lot of the fireproofing in the vicinity of the impact, which is right where the fire would be burning - a worst case scenario coming true.