Anecdotes like yours really bother me because they sound so outlandish that their veracity cannot be taken on faith. Having spent a considerable part of my working life in the US, i can state that never once has the subject of Caste ever been a topic of relevance with my Indian colleagues i.e. it has never ever come up in any discussions, implicit or otherwise. None of my American colleagues knew much about it; and i have worked across a bunch of companies so the sample space is quite spread out.