They’re what is termed a “trip-racial isolate group.” They’re scattered all up and down the east coast into the Appalachians with a few communities west of them. They tend to reside on state lines, there’s a story behind that. Other such groups would be Lumbee and mountain people called Melungeons, or “Ridgerunners” derogatorily. Some of the Lumbee have English surnames that were among the Lost Colony, so there’s a claim not just of native ancestry. The derogatory joke about them says they’re “Would-be’s.” Would be indian if they weren’t so black.
They all go back to colonial times, outcasts, outlaws, runaway indentured servants and runaway slaves, mixed with whichever tribes in the vicinity would have them. They tend to be on state lines in order to be able to jump jurisdiction quickly if necessary. That’s not just due to criminal tendencies, they’ve been pursued way back by state authorities. For instance, in Virginia, it was once illegal for mulattoes to own property so the state would take it. They’d flee into NC to get away from them.
These are very old communities, in other words, that do have indian ancestry as well as black and early settler ancestry. The ones around here have been mixed for so long that they look more Middle Eastern than anything else.
tri-racial
In the case of NJ’s fake Indians, they have no Indian DNA (and were isolated prior to independence or English settlement of the area). Also, the proximity to the border of NJ/NY is because it was mountainous, unusable terrain at the time.