Board Thread:Improvements and Issues/@comment-6961916-20130306114004/@comment-8986886-20131219183211

N-e-ls wrote: Plus, uncle (ojisan) is a way to referring middle-aged men without them having to be exactly your uncle.

That's true, as seen when Masaki addresses Ryuken's mother as "obasama" (aunt), despite them not being related. Even though the "ojisan" Kukaku referred to wasn't present at the time, Ganju understood who she was talking about. He might have simply connected the dots, since the topic was Ichigo, but who knows?