They don't understand that we never agreed to any of their TOS/policies, they don't understand that we don't use their API. What now? Things will continue normally until they can't anymore. Assume ...
This c&d wont do much since invidious didnt agree to any terms of service nor do they use youtube's API, that is atleast what the developers of invidious said on github
It seems to me that this article just describes the same situation as the github issue. I think they just used the term cease and desist. So no further escalation from what I can tell.