The very fist time you enter tho the site (or if you enter to the site after clearing your browser), you are presented with a typical "by using our page you abide to tour ToS". I shgould know, I use pluto from time to time.
And if you don't enter the site and just use a m3u file you found you haven't agreed to nothing - there is no contract.
Also, the studios that licenses the content to Pluto probably did so on condition that said content was only distributed on their page and official apps, not as .m3u8 lists.
There was no content distributed since m3u-files are just contain url's. What people did with those files is an entirely different matter.
That's why it was the MPAA (as per TFS) and NOT Pluto or Paramount the ones who requested the takedown...
Then they lied on the DMCA-request since no content they owned was in the github repo..
My takeaway from this, the studios do what they always do since the DMCA was made law, they use it as a bludgeon even on things they don't own the rights to. And Pluto, talk about being naÃve techno-illiterates to some degree. If you are going to have a free streaming service based on monetizing users habits you damn well make sure only those users can access the content the approved way with some sort of verification, whether it being cryptographic, user accounts or something else.