Because it's from chapter 7 and it's a fanmade inclination that there's some weird connection between Zoro and Kaido. Like if the argument is against Zoro defeating the main villain of an arc, the LAST thing I would be thinking about is fucking captain Morgan lol.
I'd take arguments regarding actual Ryuuma parallels and possible Dragon slaying hints over that logic lol
It's also because of the parallels between Zoro's introduction arc to Oden
how Zoro accepted the deal of staying without food for 1 month and he would be set free, despite the villains having no intention of doing so
just like how Oden accepted Orochi's deal of dancing for 5 years, when Orochi wasn't gonna leave after that
and how that's the only arc where Zoro gave the main villain the final blow instead of Luffy
and how similar it was the hostage situation of Helmeppo and Captain Morgan, with Oden and Kaido during the flashback
i think there's enough conections to make it possible