And when I corrected him the first time, he also said 'I know I read the caption'.
If you're going to call somebody a liar, make sure you're accurate.
If I show you an image of a slave deck and you say "that looks like a Yankee ship from Nantucket" when you know its actually a slave deck from an English ship, then you are either showing your southern bias by fabricating or doing your best Bill Clinton impression. Take your pick.
While your factoids regarding Rhode Island are interesting, the last time I checked, Nantucket was a part of Massachusetts, not RI.
But, if you insist:
As the late legal historian, Judge A. Leon Higginbotham, Jr. observed, Merchants from Massachusetts, the most vigorous slave traders in the world, made enormous profits from the slave trade.
- Massachusetts Historical Society
IIRC, Rhode Island probably had the largest slave trading port, but Massachusetts probably traded more slaves. Six of one and half a dozen of the other.