Caveman has it most nearly correct to my knowledge. The 'head wobble' is an acknowledgement of what you are saying. I'm not sure if it is unique to the Indian sub-continent inhabitants, but that is where I have seen it. Like the word "Accha" it is subtle and can signify different things like: -
- I understand
However it wouldn't appear to be be universal amongst all individuals from the sub-continent. My fathers family who originated from India but had been in Mauritius for some time, didn't do it at all.
I have also worked with hundreds of people from companies such as Wipro and TCS. Apparently some of these organisations put staff through programmes to educate them in the culture of the people they will be working with. That could explain why the 'wobble' is not universal in people's working experiences.
Observation of culture specific behaviours is not in itself racist or prejudiced as some above seem to be suggesting. Observation is the basis of science! How you use the observation could be seen in a racist or prejudiced way - but the OP didn't do that - he simply asked an open and honest question.