I'm not a lawyer, but I believe this is an actual DMCA notice. It has all the required components[0] of one. Is there something I'm missing? What makes this not a DMCA notice?
It's not at all clear that they have identified anything on GitHub that is a copyright infringement. They've correctly claimed that the software is being used elsewhere to accomplish infringement, but the URLs they identified aren't reproductions or derivative works of any movies.
0: https://en.wikipedia.org/wiki/Online_Copyright_Infringement_...