From the RIAA perspective it seems clear this tool was created to download copywritten material. You can disagree with the law or think the tool has other valid uses but the intent of the tool author seems clear here.
The author of the tool should have chosen a better example in the tests to at least maintain plausible deniability.
Yes, obviously there are legitimate uses. That’s not the point. The point is the actual codebase of YouTube-dl features copyright infringement as a test case. RIAA is using this to make the case that the tool is designed to aid in copyright infringement.
That seems like a reasonable argument given the evidence and the DMCA. I’m not defending the DMCA or RIAA here.
The author of the tool should have chosen a better example in the tests to at least maintain plausible deniability.