Unless this is a different person from the person who has been the cited mass downvoter every other time it's come up, they have very definitely been warned.
In some sense yes, in a practical sense I don't think so. Talking with the person more directly could be enough to get them to stop.
Below is a message I just got from jackk. Some specifics have been redacted 1) so that we can discuss general policy rather than the details of this specific case 2) because presumption of innocence, just in case there happens to be an innocuous explanation to this.
So... thoughts? I have mod powers, but when I was granted them I was basically just told to use them to fight spam; there was never any discussion of any other policy, and I don't feel like I have the authority to decide on the suitable course of action without consulting the rest of the community.