Little tendrils/roots grow down from along the branches and dig into the ground and grow a peanut at the end!
There were also quite a few tiny peanuts starting, so I harvested a handful of the larger peanuts, then carefully replanted the plant. I will give them another couple weeks. The weather is going to turn cold now and days are getting short, so they may not grow any bigger. But based on the number of large peanuts growing on this one stem, I should definitely get enough to make a jar of peanut butter!