I read this story a few months ago, it had a few more details then.

They tried giving them iron cookware, but they didn't like the weight. They then tried putting a random piece of iron in with their cooking, but not many kept up with doing it. That's where the idea to shape the iron like a lucky fish came from, and it seems to be working.

It's more efficient (cost-wise) to give the smallest quantity of iron that releases it. And it can be used in pots of different sizes

Probably but that'd be more expensive.