If in fact the terminology used is "abandoned" versus "died", this puts it in a different perspective. IIRC, initial reports the morning of 9/11 gave a figure somewhat near that number ( I know it was in the tens of thousands.) I always assumed that figure was for the number of occupants of the buildings (who would have been killed if the towers had collapsed immediately), but that number was scaled back dramatically when many were lucky enough to make it out before the collapse.
From the transcript:
"It never occurred to us that the commander-in-chief of the American armed forces would abandon 50,000 of his citizens in the twin towers to face those great horrors alone, the time when they most needed him."
He did use 'abandoned' and as you point out, the initial estimates were that around 50,000 people were in the buildings.