That sentence came across to me as implying "very likely not true", which is what would be the case in an English paper. But does it carry the same implication to Americans?

Yes.

If accurate, that suggest that the "Islamic Culteral Center" will be about 300 feet "as the crow flies" from Ground Zero, "North side X".

SO? How far is far enough? There has been a long-running fight on Staten Island about building a mosque there. This is just anti-Islamism. The people chanting "Mohammed is a pig" at the demonstration outside the Burlington Coat Factory building make that very clear. It's hatred and bile. The ruse that it's about "sensibilities" is just that, a ruse. It's about bigotry.