There IS no reason for Oda to relate Zoro to Oni three Times in a row(Onigashima, Kaido, Oni) if not to Say something.
Last Time Zoro was insulted by Luffy it was three Sword style, four Sword style.
And WE all know Zoro in fact is a 3 Sword style user and has attack named After Oni.
This comparison also happen in a moment as Big as Luffy Dream being revealed (offpanneled) and Imu destroying a kingdom.
I wont be surprised If Zoro's father was a four Swords style user while his Mom was an Oni and her name is Roronoa.
And even if Oda dont mean it literaly it Can forshadow Zoro's King if Hell narative in Wano.
The King of hell is Depicted as a Démon in bouddhism.
And in other animes as an Oni, the great King Enma.
So this isnt the last Time WE are seeing Zoro being Linked to Oni.
Look at Asura there, the Demon God behind Zoro is basically an Oni lol like Orz with three head and 6 arms.
Literaly the manifestation of the King of hell.
Asura Zoro was basically Oni Zoro vs Oni Kaido and the strongest Won the exchange.