Definition of "gratefully"

A waiter brought his aperitif, which was a small scotch and soda, and as he sipped it gratefully he sighed. ‘Civilized,’ he said to Mr. Campion. ‘Humanizing.’ […] ‘Cigars and summer days and women in big hats with swansdown face-powder, that's what it reminds me of.’

1963, Margery Allingham, chapter 5, in The China Governess‎