No Sec. XVI muitos Portugueses navegaram sob as cores Espanholas e vice-versa.
É natural que a corte Espanhola viesse procurar marinheiros experimentados em Portugal.
Como um confrade tinha referido Magalhães e Cabrilho ( entre outros) eu referenciei que eles eram de nacionalidade Portuguesa, simplesmente.. "correndo" sob bandeira Espanhola
) ( eram os "Alonsos" dessa época...
)
Quanto ao Cabrilho..
Eu baseio-me(por ex) na base de dados da "Biblioteca do Congresso dos E.U), cito(perdão por ser em inglês:
Hispanic Division: Back to Portuguese Role in Exploring and Mapping the New World Cabrilho's Discovery of California
Portuguese were also involved in the exploration of the west coast of North America. In 1542-43, Portuguese-born João Rodrigues Cabrilho and his chief pilot Bartolomé Ferrelo, who may have been Portuguese, were the first Europeans to explore the coast of the present state of California. Sailing for Spain, Cabrilho left in June of 1542 from Navidad on the west coast of Mexico and proceeded north. He reached San Diego Bay in September, becoming the first European to set foot in what is today the state of California. He continued north along the California coast but died in January 1543 from an infection resulting from a broken arm. Ferrelo, his pilot, continued north, possibly reaching the Oregon coast in March 1543.