This entire scene shows the camaraderie and bond that Luffy has with his entire crew. Anyway, I like to think that Zoro's scene was shortly after Thriller Bark and before Sabaody Archipelago. Luffy being Luffy is concerned that Zoro is still too injured to be training, so he goes and checks on him. Instead of letting Zoro know that he is concerned, he is just his normal self because Luffy knows that Zoro hates to have anyone see him as weak.