Yoo, I'm NDN, and they pretty much got it right. You eat ONLY using your right hand, drink with your left. This is cultural thing that stems back to the olden days. The thing is that indians used to wipe their a$$ with their left hands, so they only eat with their right hands to keep their food clean. It's an ancient mentality that became a cultural tradition.
In regards to how you eat the food, you generally mix any sauce w/meat /vegetables you got with rice first, then eat. With nand and uppa and such you break off pieces (remember, with your right hand only...kinda tricky at first), and then grab meat (like a piece of tandoori chicken) and such with each small piece. For more complicated dishes like idly somber you used a spoon.
But if you're at a restaraunt and don't feel like getting your hands dirty, just do whatever you feel like. Nobody's gonna hit you or anything. Even at my house I eat with utensils most of the time cause it's cleaner. In college, I eat everything with chopsticks cause they're cheaper than plastic spoons/forks.
That's pretty much the gist of it. Have fun eating yo.
Soujir0😀