“So how does this affect the national popular vote movement”
I would think that would be a different issue for SCOTUS. In that case states are forcing electors to vote against the will of the people in favor of the national popular vote. In this case SCOTUS said forcing electors to vote with the will of the people is ok.
But each party has its slate of electors who commit to voting for a specific candidate. In effect the State is changing the commitment of individual electors. It is important to read the decision to sort that out. Have you read it?