It was an air traffic screwup, mostly by San Juan Cerap, which is an FAA facility. 180 miles north of San Juan would be right on the extreme edge of radar coverage, so its likely that nonradar separation procedures were being used. The error was not charged to New York Center which controls the nonradar airpace from about 200 miles north of San Juan all the way north to New England coastal waters. I can probably find out exactly what happened.
Good thing the Russian pilot actually listened to his TCAS. Something similar happened over Germany and the pilot chose to ignore the TCAS instructions leading to a mid-air killing all aboard his plane and the pilots of a DHL cargo a/c.