You’re technically correct, but given that Columbus sailed in 1492 and discovered islands in the Caribbean, he is generally given credit for discovering the “New World.” At least that was the story when I was kid some 30+ years ago. History gets revised and refined as new sources are uncovered and reconciled with the existing body of literature/evidence. Vespucci came after Columbus on subsequent voyages that aimed to understand the scope of Columbus’ discovery. I am not sure if anyone actually referred to the previously unknown (to 15-16th Century Europeans) lands as the Americas at the time, but it’s a modern convention aimed at making it simple to refer to the lands that would be uncovered as a result of his “discovery.”