> He also ignores that a lot of Manhattan workers live in other burroughs, cities, and even states.

And this phenomenon is unknown in other cities?

Manhattan's population doubles every weekday morning. Most cities do not have either a 50% or > 1 million commuter population. Is there even any other city like that?

Yes, there are other such cities. In fact, Redmond City has, percentage-wise, an even bigger fluctuation, according to this article: https://www.citylab.com/transportation/2013/05/most-importan...