Ryuo literal meaning is 'flowering Sakura'. It means flowing your armament haki into swords.
It's obviously busoshoku haki but unlike simply coating your body and sword, it allows user to project it outward in various forms - to deflect, to create shock barrier, to make blade black and much more difficult than this is to destroy object from within.
The reason Hyo equated with haki is because wano people see this as haki itself as its a closed country. But based on basic haki we knows, ryuo clearly builds in it and one can infer an advanced version
the misconception from chapter 939 that ryuo is solely describing flowing armament into swords and the emitting technique is due to the way the conversation was structured
in 939 luffy goes to punch armidilloman and stops saying its normal COA
hyo asks why he isn't punching them and luffy says he wants to push them back without touching them ( advanced technique) and that he's seen it before and it's still regular armament haki
hyo goes on to say that this haki you call it we have an abilitly like that transferred from the users body to the sword(COA)
hyo mentions it allows them to cut thickest steel or if they want not even cut paper(what zoro did back in alabasta, which he was unconsciously using COA) he goes on to say he learned it from a swordmaster( at this point he's talking about ryuo/regular armament haki)
he then says don't know if i'll be able to teach it to you ( referring back to what luffy mentioned when trying to punch without hitting, the emitting technique)
hyo then uses emitting COA on alpacaman and asks luffy is that is what he was trying to do
your right about the literal meaning of ryuo and what we leant from the whole luffy/hyo scenes from chapter 939 and 940 is that COA is used by flowing your haki around your body, into your fists or weapons such as swords concentrate that flow and you can harden your fists or weapons (hardening COA) then you have the two more advanced techniques, emitting your COA (flowing it outwards) and flowing your COA inside an object destroying it from the inside
you right in that the emitting technique and destroying object from within is haki and therefore ryuo
but ryuo isn't the specific term describing only those techniques it's the wano term for all armament haki