Why do Injera recipes call for adding boiling water or cooking down tef with some water? Very often in Injera recipes you will see step toward the end of the process, right before cooking that involves cooking some Tef flour with some water and then mixing that into the batter. Can anyone explain what this step is for?

The rough recipe I'm thinking of works like this (also see here:

1) Mix equal parts Tef sourdough starter and Tef flour. Let that ferment for some days.
2) (optional) Mix some more Tef flour into the dough (1 cup) and then wait again.
3) Mix 1/2 cup Tef with 1 cup water in a pot and cook until it thickens, while whising. Let it cool. Then mix it into the batter.
4) Add water slowly to the batter, while mixing, until it is quite thin. Let it ferment again until small bubble form on the surface. Then it's ready to bake.    

It's the step #3 that I'm wondering about.
I can’t give a definitive answer for Injera, but in baking, a boiled water/flour mixture (called tangzhong or  water roux) is added to increase the dough’s water content, effectively binding more water in the dough than a plain dough could. The results are typically very fluffy and light. 

I suspect that Injera with this water roux would turn out more pliable and a bit softer. Considering that you use bits of it to scoop up the stew that is usually served with, I would expect it to be more “bendable” and texture / mouthfeel would certainly also benefit.