It just says that he could have been born in Spain, not that he was.
I'm sticking with Columbus being from Genoa, Italy before anything.
Even though he never visited Italy or never wrote in Italian and was never heard to speak in Italian.
Not that he had much time to do the first one in his later years (and the last one is unprovable.) The traditional Genoese accent is very close to Catalan anyways, a fact that escaped this guy.
Such theories have always existed - I once came across a theory that Columbus was Chinese - but I wouldn't believe them on such flimsy evidence - although I wouldn't want to rule it out quite entirely.