"Columbus "discovered" a land "
Yes he discovered it. To his people it was a discovery. I get somewhat tired of this really pedantic interpretation of the word "discovered." Hundreds of years from now will we will probably have people saying "No, Captain Kim did NOT discover a habitable world around Rigel because there were already beings living there!!!"  It's just a really, really pointless objection. If you find out something you didn't know before it is a discovery. Just deal with it.