Oda explained that one away in some SBS. "He was just imitating the others".
No, Oda said Luffy is "interested but not entranced" and that he has a "bad side" that Usopp brings out. There's zero mention of Luffy imitating anyone.
Even before that in SBS 32, Oda was asked why Luffy, Usopp and Chopper peeped and he simply said "Why, you ask? Well, that's because they are all healthy boys. I don't think there needs to be any other reason than that. But for Chopper, he might have done it just because everyone else was."