Indian English is not the same as American English. As I understand it, "backwards" means "disadvantaged" in this context. Perhaps you should prepone learning about English dialects.
And it just happens to have a more commonly known negative meaning? They could have picked disadvantaged or oppressed, instead, for that acronym. I had little-to-no idea about this system until today and I'm not even a native english speaker, but all the same it seems curious to me that this word choice is just a coincidence...
Who could have picked those terms? OBC is a term of art used in Indian politics [1]. The author didn't exactly choose that term.
And OBC is Indian English, which is one of the most common varieties of English spoken worldwide. I think it's really weird when people say "carpetbagger" in American politics, definitely more weird than OBC. And don't get me started on the racist origins of "grandfathered in" or "eenie meenie miney moe".