To be honest, I never noticed anything like this on a recent non-stop to India on American Airlines, even though the vast majority of passengers were Indian, on both the inbound and outbound segments.
My experience with Indians is it is not so much that they don’t bathe or whatever (actually, I think they don’t as much as westerners), but it’s their diet!
The garlic, the curry and other spices...when people load up on that stuff, they can reek even when they come out of the shower.