In his original GitHub issue comment (https://pbs.twimg.com/media/E6p_DcrUcAMWFtB?format=jpg&name=...), he seems to imply that the author may be criminally liable, though he doesn't actually explain how or why. Seems like it may just be a way to bolster the intimidation attempt.

Criminal copyright infringement is a thing, but I strongly doubt it would apply here:

>There are four essential elements to a charge of criminal copyright infringement. In order to sustain a conviction under section 506(a), the government must demonstrate: (1) that a valid copyright; (2) was infringed by the defendant; (3) willfully; and (4) for purposes of commercial advantage or private financial gain.

Even if one assumes for the sake of argument that (1), (2), and even (3) are actually met, (4) clearly doesn't apply. And based on all of the author's statements, I think it's unlikely (3) would be met, either.