People are either being completely disingenuous, or they don't understand that City of London is a relatively insignificant portion of greater London. This fact alone illustrates how absurd the comparison actually is:
> As of the 2011 census, the City of London has a population of 8,072 and area of 1.12 square miles.
(For context, Manhattan has a population of 1.65 million people, with about 73,000 people per square mile. Even setting aside that lower Manhattan is more densely populated than upper, and that a lot of people commute in from the outer boroughs, the congestion pricing scheme would have affected at least 800k resident people, or about 10% of NYCs total population.)