According to google, Favreau is indeed from Forest Hills, but Scorsese actually grew up on the other side of the East River in Little Italy. Apparently he was only born in Flushing, and his family moved a few times when he was a kid, but Elizabeth Street in Manhattan was the main fixture.
So maybe Scorsese is just imitating Favreau's accent? I've honestly not seen enough interview footage of Scorsese to get a sense of what his natural accent sounds like, assuming my ear could even tell the difference!
Either way, it does feel like a conscious choice to make Ardennians sound like New Yorkers.