There is a theory that he was a descendant of conversos (Jews who converted to Christianity) but he was not Spanish, he was an Italian from Genoa.
I don't know what "Messianic Jew" means in this context. Conversos were Jews who observed Christianity in public, but continued to practice Judaism secretly. They would more accurately be called "Judaizing Christians." A "Messianic Jew" is someone who claims to be practicing Judaism, while believing in Christianity. (I exclude from the definition of "Messianic" ordinary Orthodox Jews who believe that the Messiah has not come yet, but expect the imminent arrival).