Interesting how you mention the need to heat the iron well you would need to know about it first wouldn't you so that means, by your own logic, that the Indians did use iron furnaces or something similar to heat the iron to then shape it. So my case in point.

Why would anyone want to spend all that energy shaping iron beads with a rock the size of his head?

They had something similar to a furnace called burning wood. Not that it's required, I was just saying it would help. And assuming that the meteorite they're pounding would already be roughly spherical, it wouldn't be too difficult to round it out. And I'm sure to an Indian would consider it worth his time to experiment with the magic rock that fell out of the sky.

First you would be hard pressed to find a small meteorite at all let alone twenty two and it is even more rare to find one remotely close to being spherical. Wood does not produce enough heat in itself to make iron hot enough to forge with rock one would need a furnace like structure to keep the radiation focused in a small area. And if magic rocks fell from the sky than I believe they would have tried to worship it and not change it.