Oh god, I think I do this. Not specifically to South Asian people, or people of a particular ethnicity - I just mean that I am terrible at recognising people in general.
This means that when I meet someone I deliberately take note of something about them in order that I’ll be able to identify them next time (eg the man with red hair, or the woman with purple glasses, or the girl with the big nose, or the South Asian-looking man, or the woman with very pale skin, or whatever).
While this does help me identify people much of the time, I get into terrible trouble if it turns out there are two women with purple glasses in the office, or two South Asian-looking men, or whatever. I’m sure people might think it stems from racism where I confuse two people of the same ethnicity.
I really hope not - I would hate to be offending or upsetting people. I just really am DREADFUL at telling people apart and if I don’t latch on to a key characteristic of theirs, I wouldn’t be able to recognise them at all. In fact, I once mistook my own brother when I met him by accident at a bus stop, but that’s another story.