I would say, "none of the above."
Seafarers had known the Earth was, at least, curved, since the time of the ancient Greeks and, likely, before. Anyone watching a ship disappear over the horizon could figure out the the Earth was, clearly, not flat.
If he was the first person to reach the Americas, then who were the native he met when he landed?
As far as Europeans, it's been pretty well established that Norse explorers had settled in parts of Nova Scotia about four hundred years before Columbus was born.
And, as far as navigation, his strategy was to simply sail West. Whether he reached what he hoped was China, or the Indies, or landed on North or South American soil, he was BOUND to bump into something. Even I could maintain a vaguely Western course, using nothing but the light of the morning and afternoon sun.
Columbus' "genius" was in being able to convince Queen Isabella of Spain to hock her royal jewelry to finance his trips.