We got a full arc with BM and something like this was never said about her.
Oda wouldn't throw these type of absolute statements randomly. It wasn't a gag or someone from beast pirate who said this. Maybe it doesn't have the same weight as as an infobox but for me it's enough to put Kaido above any other pirate alive until proven otherwise.
I would put Kaido above anyone else because individual strength here is debated in this even when WB was alive he was the strongest creature and it makes sense he is a dragon and dragon are generally the strongest
it also makes plotwise sense that Kaido is the strongest being in earth otherwise Luffys victory would be overshadowed by Garp and Rogers so Luffy need a feat that needs to overshadow Rogers
and this feat is beating the absolute strongest being in earth
Kaido is set apart from others he isnt considered a human he is a creature amongst all living beings in earth
humans, animals , dinosaurs and so on , in sky no bird or something else is stronger and sea sea kings, whales and so on is not stronger than him he is the Apex predator he stands at the top of the chain thats the interpration of Kaido
also in his introduction you could read it the strong live the weak thats how the nature works and Kaido is simply too strong too die