I think John refers to Cabot reaching the continent of the Americas, not the islands. Columbus actually only arrived at the mainland (Nicaragua) in 1502. In fact, the discoverer of America, including the islands was, wait for it, drumroll, fanfare: Gunnbjorn!
G. discovered Greenland, which is part of North America. He then told Leif's father Erik the Red who explored it and named it Greenland. (An early real estate developer)