I think I read too much into his quote. What threw me is that Prof. Barton was sloppy with the way he phrased it. He said more than half of the states in 1776 abolished slavery, then listed only six, and the way he said "four in the south," instead of all southern states or something similar, made me think he had switched in mid-sentence to a later time period.
You're right about Princeton, but, to be 100% accurate, it was called the College of New Jersey at the time. My screenname refers to Henry Lee II who, although a College of William & Mary man, sent his two oldest sons, "Light-Horse Harry" (Am. Rev. hero, governor of Va., U.S. Rep. from No. Va., and father of Robert E. Lee) and Charles (the second U.S. Attorney-General under Washington and Adams) to the College of N.J.
No disrespect intended, but a BA + an honorary doctorate does not a professor make.