Of course wallaah & babu are from India; that's where I was living when I learned them. The Old India Hands were mainly of British heritage, their links w/India from the days of the British Raj. They always said the origin of Babu was as I quoted. In any case the modern usage, whatever it's origin, was much broader than clerk, of which there are seemingly zillions. Just about anybody could be addressed as Babu, & beggars always addressed people as that; even me, the Pukha Sahib from America.

Cheers, BK