Why did Hannibal assume Jinbei had never met Hancock?

That was later. Hannibal entered first and introduced Hancock who followed, and when he introduced her he 说 he says Jinbe hasn't met her before. I can't figure out why.

Yeah. It wouldn't exactly seem like an assumption - he would have known that Jinbe was a Warlord previously, so there's no reason for him to not think that they had met, even if it sounded like they didn't. I wonder if Hannyabal had intel on it, 或者 something... maybe he listened to something he shouldn't have, Either way, I don't really understand that one. Even after watching it.

Actually, there is absolutely no reason to think that Jinbe and Hancock have met before. I mean, clearly they've heard of each other before, but they simply never got the chance to meet. Neither ever 显示 up to the Shichibukai meetings (most of the ones who attend, like Doflamingo and Dracule, only go on whim) and until the battle in Marineford, there supposedly had never been an event that called for gathering all seven of the warlords together. So they simply haven't met until then. That's all there is to it. All that aside, Jinbei is a fishman who only took the position to protect his fellows while Hancock is the leader of a tribe of women and rarely ventures outside the calm 带, 皮带 without good reason. Them meeting 由 chance is also very slim.