I can't imagine someone thanking the French for baguettes or the English for crumpets after winning there
Why stop with cuisine though? Djokovic and Nadal could have talked about kangaroos and wombats in their speeches at the Aussie Open.
I think Milos was thanking the tournament organizers for doing a good job in catering, for serving tasty sushi which happened to be one of his favourite food that originated in Japan.
I don't think there's anything wrong with thanking the French for baguettes either if you love'em to bits.
Baguettes and crumpets IMO are arguably less distinctive though.
Sushi OTOH is also viewed by many as a culinary art, sort of like French's haute cuisine?
But koalas, kangaroos and wombats isn't really "made in Australia", they're just animals living in their natural habitat.
I guess it's each individual's personal interpretation of his comment.
To me, it just sounded like a token of respect.