Are you sure? Here's when Zoro and Killer cut Kaido. You can see the specks of blood and Kaido's grunt of pain:
It looks like blood to me. Furthermore, in the next panel, we see Kaido feeling the attack. Afterwards, he compliments the both of them:
Why didn't Kaido think about:
- Big Mom
- Is Mama unable to damage Kaido.
- Garp
- Sengoku
- Blackbeard
- Is Blackbeard unable to hurt Kaido?
- Rayleigh
- We know Rayleigh can hurt him because he possesses internal destruction COA.
The five silhouetted with Luffy were simply the people that beat Kaido or grievously wounded him.