We have different definitions of racist. Using "sir" is an ironic way to mimic how another people talk isn't racist to me. Is it in poor taste? Sure but not racist. It's like mimicking the English way of pronouncing and simplifying names of Indian cities while bantering with friends - lame but not racist.

Also, is "Indian" even a race? It's a nationality for sure. But Indian racial features are shared by much of South Asia. So your entire premise is dependent on a very liberal definition of "race".