You aren't technically wrong but these claims are made out of regional pride. Many regions have claims to be the authentic homeland of Columbus, like Galicia, Catalonia or Mallorca. Bona fide spanish nationalists have no problem with him being italian at all, as he was still serving Spain. Italians doing great service to the spanish crown was a common sight these days (Andrea Doria, Spinola, Farnesio, the marquis of Pescara...)