im a bit behind so im not recognising the samurai character you're referencing but in-universe, which for this argument is the only position that matters IMO, zoro's sword abilities are not presented as any kind of supernatural, extraordinary perhaps, in the same way IRL that olympic athletes' feats are extraordinary, but not supernatural, people can just DO THAT in the world of one peice with no magic or special powers if they put in enough effort, zoro isn't using some special sauce to pull off his techniques except a hell of alot of weight training.
i'm very tired of this coming up every time this topic is broached, extraordinary martial techniques getting 'no true scotsman'ed' out of actually being considered TRUE martial techniques because they've become impressive enough that people decide 'well those can't be martial techniques just look at what they're doing' so they instead get assigned as 'it's not magic but no wait actually we are functionally considering it magic afterall with just a different name' '''supernatural'''