He did not sense Oden in the scabbards, he said they were using his kind of Ryou and that made him remember Oden.
The spoilers specifically say Kaido senses Oden in Zoro's SWORD, not that he is equating Zoro to Oden like he did the Scabbards, and Luffy.
And what battles has Kuina ever been in with Wado outside of one time she fought Zoro as a child that would constitute her being a fallen solider, whose blade retains her spirit?
What do you mean? What the difference here? If the Scabbards are using Oden’s Ryuo and Zoro is using Oden’s sword, what’s the difference? If you are saying Kaido can like sense specific souls, like he has this higher level observation haki to sense individual types of souls in objects then when he says, “Oden is in that Sword” and “That is Oden’s Ryuo”, isn’t he using his ridiculous observation haki to say that the scabbards are literally using Oden’s haki and Oden is literally in the sword.
So are the scabbards literally using Oden’s haki?
And Kuina’s trained with wado, she didn’t just pick it up for the first time when fighting Zoro, and Oda has even said in an sbs that the sword carries Kuina’s memory, so why wouldn’t it also retain her literal soul?