I suppose this may be a difference in cultural attitudes.
In the US, you are encouraged to be different. Standing out from the crowd is how you compete and become employable (and not blend in). The thinking goes - if you're just like everyone else, you're a commodity - you offer nothing of real value over and above a minimum threshold that someone else could easily be a substitute for. However, if you stand out, you can extract a premium value over others.
In India, maybe it's the opposite? Perhaps the advice you've been given comes from the attitude that to be employable, you need to fit in (be like everyone else) rather than stick out. That could be one of the factors why so many Indian males are force fed into engineering. Again, someone else could shed light on this (I know that in India traditionally given how stratified Indian society is, engineering was one of the only professions that was based purely on merit (other than medicine maybe) so that is why it ended up being the only choice for people from modest backgrounds to move up the economic chain -- hopefully that is changing though and there are more opportunities).
So it really depends on context. In India, it might be true that you'll be less marketable because of your NGO background, especially in an environment where everyone is expected to be an engineer if you aren't wealthy, can't play cricket or sing/dance like a Bollywood star. In the US, it would be the opposite - also partly because philanthropy and the social sector is magnitudes larger (and has more money swimming around) that you can make a living working purely in the social sector (which there may be far less opportunities to do so in India).
Ultimately though, it's a case-by-case basis. It's more of a gut feel that an adcom will have when evaluating cases like yours which are more unusual.