User blog comment:12th Supernova/Chapter 815: Germ Warfare/@comment-24850639-20160204161726/@comment-207.164.187.162-20160204205807

In fact it's more like Pekom is calling back Luffy, not Zoro calling him Straw hat.

Law is also the one that wants to talk to Luffy, what he tell his crew afterward tend to reinforce that impression. We then cut to a scene inside with Law reacting to being told what happened to Sanji. We don't know how much time happened between the two scenes. Law may already have told Luffy want he came for and we will learn about it in a flashback later.