This is a gorgeous story. After living in a small town in Thailand — where I learned much, much less Thai than you learned Bengali — I know this specific issue of change. But it was Thailand, not India, and a town rather than a rural village, so it managed to fit in a whole slew of 7–11s. The minute you got your 1000-baht bills, you bought a soda or ice cream at 7–11 and got all your small bills with which to buy 20-baht jook. (alternately, be a good bank customer and smile a lot when you ask for change but no other services).
As for the REST of the story…yes yes yes. I love these small moments. “Kindness despite strangeness and kindness requiring no reward.” It’s unfortunate that it occurs somewhat more across cultures…when you’re abroad, or meeting foreigners at home. I’ll admit I find it much more charming in those situations as well, and it’s one of the things I personally love about traveling, or about interviewing immigrants. But it shouldn’t be restricted to that. We should all be kinder to each other without the excuse of cultural exchange.