It's actually just a standard 4-40 thread cut into the filament. They use rollers to prevent rotation of the thread when cutting the threads into the filament, and then when they actually use the nut it's got enough thread engagement that it's better than a hobbed gear. If you think about it, it's almost like a hobbed gear that attacks from all sides instead of one or two.

Feel free to ask me questions on it, I work in the industry and have spoken with one of the authors of the paper, it's a shame it's behind a paywall.