Rav Schachter read the story in the book "Operation--Torah rescue: The escape of the Mirrer Yeshiva from war-torn Poland to Shanghai, China" by Yecheskel Leitner, page 68.
Here's an excerpt:
There was also a striking contrast between the conduct of the yeshiva passengers and that of the other people on those trains. In the words of a western European fellow passenger who was unaware of the unique status of the scholars and Torah giants with whom he lived for two weeks on the Trans-Siberian train:
They showed a puzzling kind of conduct all day, con-stantly arguing with each other — but in friendship! Quarreling and disputing, even in larger groups — but only verbally! Their heated disputes focused on oversized books, large bulky volumes from which the disputes seemed to originate or to end.
As striking as this observation might seem about the manner in which the remnants of the famous European Torah centers spent their days on the trans-Siberian trains, that observer could barely appreciate the high scholastic and religious standards of his fellow travelers, who spent their days of miraculous rescue in the study of Torah. They were absorbed in trying to solve numerous problems of legal, ethical and religious character arising out of the changing conditions and the technical innovations they were encountering during this trip. These new facts had to be assessed according to the principles of Torah living. The heated debates were testimony to the depth of commitment of those individuals to the obligations and principles of Torah life.