It's true most of his comments are pointless, but so is this thread.
Oda introduced Koala as "Revolutionary, Fishman Karate substitute teacher".
Young Koala spent a long time with fishman pirates, plus the color scheme in volume 75 resembles the young Koala.
Also, she was introduced along with Sabo. It's hard to miss her when she appears with a person that rose endless discussions about his past, "death" etc.
If you're not up to date with the manga, keep in mind that OP section is dark and full of spoilers.