Being from Wano or another country does not matter
The thing Kaido was talking about is the there will be no any samurai like Oden
Samurai does not mean only from Wano thate whats i am saying to you
Those who follow the way of Sword are Samurai . Zoro was taught swordsman ship from a person from Wano . Thats what matters
It does matter Kaido didnt refer to all samurais around the world he was referring to the wano samurai also there are no known samurai country beside wano not all swordsman are samurai lol
He wasnt thought the doctrine of Wano he was just thought how to use a samurai and he did create his own three sword style just because his teachers father was from wano doent make Zoro a samurai
Also it was an blacksmith not an samurai who fled the country 50 years so Zoros master isnt technically a samurai
Zoro isnt in this reference of Kaido he just meant all samurai in wano
Also wanos samurai differ from other swordsman
Lol Kaido clearly meant all samurai in wano because he knows them but he doesnt meant pseudo wano samurais like Zoro