Neville ChaimBerlin:
“I think it’s based in the way they’re partitioned. If there were no barrier between KGH and downtown Flushing (Mandarin Town) then I presume there probably wouldn’t be an eruv in KGH because it would be considered one town with well over 600k people. My understanding is that the LIE is essential in allowing there to be an eruv in KGH. The boarders between Flatbush and surrounding neighborhoods have no physical barriers like highways; they’re just random, so they might all get counted as 1.”
Rav Moshe never made the distinction of the LIE, and it is irrelevant according to his shitos in eruvin.