Well, he could be the "swordsman king", just like there is a "pirate king" title nowadays without an actual pirate kingdom. Wano isn't mentioned anywhere in "Monsters" either.
Yeah, we haven't sufficient canon info to affirm for sure, but the evidences point that Ryuma was famous worldwide (therefore, he must've left Wano at a certain point of his life). Even the recent "Monsters" (103 Mercies Dragon Damnation) adaptation, supervised by Oda himself, didn't change the village's design to resemble Wano's. The original Shusui was "retconned" to be a black blade, but almost nothing else changed.
Yeah, we haven't sufficient canon info to affirm for sure, but the evidences point that Ryuma was famous worldwide (therefore, he must've left Wano at a certain point of his life). Even the recent "Monsters" (103 Mercies Dragon Damnation) adaptation, supervised by Oda himself, didn't change the village's design to resemble Wano's. The original Shusui was "retconned" to be a black blade, but almost nothing else changed.