"a tinkling, Chinese melody, which made a boy in the line along from me stand up, and call out, 'Ninky-poo!'"

Probably a reference to Nanki-Poo, a character in The Mikado.

This comic opera by W.S. Gilbert and Arthur Sullivan opened at the Savoy Theatre in London in 1885 and ran for 672 performances. 

(Ninky Poo is a character in the 1940 film Road to Singapore.)