I've said it before and I'll say it till my dying breath - so what! It isn't who has visited or who has been blown over, it is the person who started the conquest that counts in history.
It is a pretty solid fact that Erik the Red, his son Leif Erikson and their friend Bjarni Herjólfsson led a Norwegian/Icelandic exploration & settlement of Greenland and the Canadian Maritimes around 1000 AD. The Greenland settlements lasted for several centuries.
Phoenician writings have been found in the US Midwest and Norse Runes in Minnesota. Ancient Chinese may have landed on the west coasts of North and South America. So What!
Columbus wasn't a flash-in-the-pan. He was followed by all of the European explorers to the end that countries from Sweden to Portugal had American colonies. Hint none known or detectable from Islamic countries!
With such knowledge, a fleet of Moorish vessels could have easily traversed the Atlantic to the New World with just as much navigational knowledge as Columbus did in 1492.