It was some tiny slip up I didn't even notice, generally we were using disinfection but not as paranoid as first time. Ie catch some rail in the bus and then eat chapati with that hand, or maybe we hit some dhaba/restaurant that didn't have everything freshly cooked. Mental fatigue over time gets you, especially when in challenging environment.
Don't take it as negative comment overall, I can't express with words how much that backpacking experience there meant to me. I came back as different, dare to say a better person but listing reasons would take tons of time.
Love the culture, history, various coexisting religions, common people were always very kind and helpful, and overall intensity, even with few negative aspects. Learning to haggle a bit was very hard but it paid back itself later in life tremendously, ie managed to haggle down 60k $ from the price of apartment we bought from one CFO of major insurance company where I live now. Wouldn't have balls to do it without that experience. But whole list is massive and many things I don't even realize myself and never will.
If I understood you right, this was because you didn't sanitize your hands the second time?