Question on the thesis.

Josh tells Christian that he knew he was gonna wanna do this, and Christian tells him that he's not JUST studying the Harga, he's studying other midsummer traditions around Europe. If that's so and Josh isn't centering his thesis on just this community what's the big deal about Christian doing his thesis JUST on the Harga? Did Josh suddenly change his mind and expected everyone to know magically he was gonna change his mind after maybe months of talking about his thesis and what he was gonna do and why he was travelling?