I think it's one of three options:
1 - He doesn't have a black blade and it's just a drawing mistake.
2 - He has a black blade, but he took it from someone else he killed, so he doesn't care about it, he just uses it as an accessory on his waste. He didn't forge it.
3 - He has a black blade, but it belonged to someone he cared about that died, so he keeps it with him. He didn't forge it black. Could be the woman hinted in his tattoos.
1 - He doesn't have a black blade and it's just a drawing mistake.
2 - He has a black blade, but he took it from someone else he killed, so he doesn't care about it, he just uses it as an accessory on his waste. He didn't forge it.
3 - He has a black blade, but it belonged to someone he cared about that died, so he keeps it with him. He didn't forge it black. Could be the woman hinted in his tattoos.
He could have just have given him a meito, even a Saijo, you know. There was not an armed man threatening Oda.
But again, this is Fuji 2.0.
Before the Saijos were the mark of excellency; Fuji gets one and suddenly that doesn't mean much anymore, some user still put Oden above him even if all Saijo users were put above him before etc.
Now is Ryo's turn. All BB users forged it or were mythical descendant of the one who forged it and destinated to do the same and became WSS; now that an admiral does, suddenly he becomes the first exception in the manga of "yes, he has it, but it's nothing serious; it doesn't mean much".
People legit create imaginary forged of BBs rather than saying that Aramaki, a top tier modeled after Gennai Aramaki, a genius swordsman of Roningai, forged it.