Greenbull pulled up to the entire group dude.
Forget Kaidou he pulled up alone to a group that took down the entire beast pirates including Kaidou + Big Mom.
It makes no sense for him to be afraid of Kaidou, he's walking in letting his presence be felt against all of Wano and the entire alliance worth 2 Yonkous + 1 Yonkou crew. Injuries don't even begin to make up for such a massive advantage for the alliance, and he pulled up a whole week after the fighting too.
If Greenbull is afraid of Kaidou is what you got out of that you're only reading surface level.
You're coping
Greenbull himself admits that he wouldn't come if Kaido was still pesent
He didn't mention Kaido's crew (he already mocked Kaido's commanders being weak ..so nope)
Unlike with Shanks where he mentioned RHp too, GB hyped Kaido's presence.
He went to Wano thinking he would get to Luffy easily cause they're weakened
That's why he didn't even want to fight retainers, he asked them to give him/let him see luffy
Greenbull is retardedly wild, he was underestimating Luffy
Anything you say is just headcanon and copium,
Oda even want on making Nekomamushi say that "that guy was right, Kaido's presence kept powerful enemies away from this country" which confirms once again it was powerlevel thing
Greenbull admitted inferiority to Kaido and Shanks made him quit