It is in America, for the most part. You can absolutely organize to harass people if the harassment is in the form of verbal abuse, for instance. Cloudflare is saying that something happened in the last few days on KF that was a genuine "emergency". I don't think this is just an excuse, actually – Prince seems unusually committed to honesty about this sort of thing. I presume people were organizing specific violent acts on KF, which is not "free speech" even in America.