You literally made the opossite conclusion, lmao. This directly proofs Kaido isn't considered a human and his title may just be tied to his race being the strongest, now it makes sense why WB could hold the WSM title simultaneously to Kaido.
In the cover, Usopp is telling his adventure story to members of a publishing team (2 shocked birds that are taking notes in a notebook and an octopus that is typing in a typewriter). Usopp is dressed as a pirate captain (he wears a hat like Roger's but with his own Jolly Roger) and on his head is a paper that the octopus has written where it reads "Big liar story".
The ambiguity is from viz's translation. Seibutsu means "living being" afaik and in Japanese the context is really clear. Kaido is said to be the World's Strongest Living Being.
The confusion comes from the part where it wasn't added to the title card of Kaido but insinuated as rumours ~ "rumoured to be", "said to be", etc. This chapter, however, makes it clear IMO. Kaido top 1 in the verse right now probably.