This is not much different from noting someone is gay in a middle eastern country and pondering what would happen if they were outed while trying to coerce them to do what you would prefer.
He created a client to consume a public API not much different than youtube-dl for sheet music which can be used to download both works under a free license or under a non free license. If the usage is infringing it is infringement by the user of the works of someone like Sony. Muse has zero call to start some shit directly with the developer because they aren't the injured party and he's not the responsible party which is why they had to stoop to nonsensical threats.
This is also why the repo is still up now.
I interpret it slightly differently, I asked the question because I was genuinely interested in others reading of it, rather than trying to push a perspective