That would make Zoro and Kuina cousins
I don't think there was ever any implied love there lol. Its not weird at all. Anyway, I think he's Ushimaru's son (who isn't directly related to Kozaburo). When Wano fell (which was 20 years ago, which was around Zoro's age being 21), I could see Ushimaru sending his son and maybe his wife to East Blue to be with Kozaburo and raise him there. Especially if wanted to save his son from a life in Wano.
Idk, if YP is pretty hyped about the chapter, then I'm not sure its this anyway. Just a theory.
Like this is literally Zoro with a mustache (its not a big frown):