Robert Birt, I rechecked the 1790 Wake County NC census, andchecked the hand writing and determined that the name listed is Joseph "Jim" Fisk and not "Joseph Jr. Fisk" and having determined this, I am sure he is not of the Lexington Ma line of Fisk. Unless "Joseph Jr. Fisk" and Joseph "Jim" Fisk are one and the same.
BTW, I looked at the whole 1790 Wake census and found two other Fisk families in the same county. James and John Fisk with families of 10 and 16. They can be found on image 6 and are very likely related to Joseph Fisk.
I would love to link my line to the Dr Joseph Jr. Fisk line, but I feel I would be doing myself a disservice if I did so.