2) Rav Moshe was led to believe that both BP and Flatbush contain a population of over shishim ribo. This is factually incorrect, as the population is less than half.
Source?
Rav Moshe in this teshuva counts from the water up to Flatbush. No mention of Boro Park. Which was then significantly less populated than the waterfront, and only estimates 350K. He then goes on to summarize why this could be considered 600K according to some Rishonim. That pretty much disproves any possibility of demonstrating that Rav Moshe was fed misinformation.