Surf & turf was me. And I am spectacularly ignorant of the vast variety of Indian cuisine, but I would be surprised if literal shells is a common staple. It doesn't say "calcium," it says "shells." And it shows a picture of what looks like a cluster of mussels, although it could be clams.

Nobody in the US eats shells like that, except for Blueshell crab almost exclusively in the mid-Atlantic region. There are some recipes where you cook crab whole until the shell dissolves into the soup, but in neither case is the point to eat the shells - they're just along for the ride to get to the meat. And if it's a source of the calcium that's sometimes added to some food, it'll say "calcium," it won't say where it came from.

So: you're claiming that it's common in India for people to, what... source and grind up shells and eat them? I suppose if folks are doing it to Rhino horns, that's not the weirdest thing I've heard. I think it's just more likely it's referring to shellfish.