Well it's revealed later that yoshino knew all about his plans involving nao and shutting down the prostitution ring that ozo was trying to rope her into. She knew about ozo and nao. And a tracker or a bug planted into the keychain way before she reveals that she knew all along that he was dealing with all these shady things would explain how she obtained such knowledge. Thinking about it now though, I think its just because of her networking skills and the fact that her grandpa controls the whole Osaka territory, so it was in her power to have gang members help her retrieve the information too. She also might have more influence in her mafia family than we know of.