yea but that doesn't mean the place he was attempting it was random.And from what the narration stated, he knew that fall definitely wasn't going to kill him.
Sure he was "trying" to commit suicide but this is too much of a coincidence.
when he landed it said something alike "so this doesn't work either"
so while it's a hobby for him,he wasn't sure he was going to survive,so it would be really strange for him to make that part of a plan of attack
also,the alliance was gonna attack shanks,not kaiodu,so he had no reason to go and attack them
as for it being a coincidence,well,it is,just like many other things in this manga (or in either other story),but we still have to go by what the story says,and kaido seemed to have no motivation to attack and no interest in the three captains when he landed
also,knowing apoo,it's not that strange of an idea that he would decide to serve instead of getting beaten up..the prideful one of the group was kidd,that if we have to take on account that boot,it has now been taken prisoner.