Do people realize the difference between "ancestry from" and "citizen"? If you are a Japanese American whose family has been in America for a few generations, you are not a citizen of Japan, plain and simple.
The reason why the distinction matters is because warriors in Wano have codes and a culture they follow, which Zoro doesn't follow. Everyone who called Zoro a "Samurai" didn't know he was an outsider. People in Wano assume everyone around them is from Wano. If Mihawk landed on Wano, they'd call him a Samurai too but he's not.
The reason why the distinction matters is because warriors in Wano have codes and a culture they follow, which Zoro doesn't follow. Everyone who called Zoro a "Samurai" didn't know he was an outsider. People in Wano assume everyone around them is from Wano. If Mihawk landed on Wano, they'd call him a Samurai too but he's not.