If we're assuming that the flashback is relevant to his thoughts in the fight with Luffy and not just for the sake of the readers, why is he remembering getting sold out by his government and not actually anything else related to Joyboy? We have no idea why he even thinks Joyboy would be someone he meets.
peep the top right panel before the flashback
did you read the king fight
the flashback on how he met kaido leading up to the promise he made to kaido as he loses
similar occurred here
"We have no idea why he even thinks Joyboy would be someone he meets."
you dont not we
he got the idea from yamato after echoing some of what was written in oden's journal
if you believe kaido hasnt accepted defeat, then you believe luffy hasnt won.

