i was curious about that one - possibly disinfo designed to undermine the position that it was a concerted effort to bring down the buildings?
If so, surely there are more buildings rigged with explosives? Also, what was the triggering mechanism - they fell perfectly that day, with that dual xcollapse ( out, and down to disguise the sequence underneath the mushroom head)
IMO, this info is probably up there with that other WTC designer who changed his position right after 9/11 from previousinterviews, to support the official story. however, there was the 1989 statue of liberty thing - where 'they'll be bringing down that tower in 10-12 years anyway' which kinda rings.