When someone treats you for breakfast, lunch or dinner, it's a custom for Japanese people to say "Gochisou sama deshita" - ご馳走さまでした。(in Japanese characters) after the meal which means "Thank you for the treat", and it is one way of showing that you really like or enjoy the food. Usually, You can observe this custom when you are going to Ramen house or any Japanese owned restaurants in Japan.
I remember that I never fail to say this word every time I eat for dinner after work at Ramen shop beside the train station at Kawasaki, Japan.