Considering youtube-dl isn't doing anything a web browser accessing these sites can't do, essentially serving as a headless web browser with a convenient CLI, I don't see how this could possibly have a leg to stand on. It's like serving Mozilla a DMCA takedown for FireFox. I however welcome the highly visible reminder that github should only be used as a mirror at most.
Yes, you can download the full video with a browser. Yes, you can use wget or curl to do that. But youtube-dl's community was dumb enough to give clear cut examples of downloading copywritten material, which is obviously not what the RIAA or probably even YouTube's lawyers want.
Courts care about intent, and it's a straw man to argue that technical similarities mean they're half-assing their enforcement.