I don't think it was a pre-planned PR stunt. There had been a lot of discussion about the issues involved between high profile Apple writers yesterday. Gruber published some blog entries about it, Rene Richie did the same on iMore. There were several heated threads on Twitter on Sunday. Taylor Swift nodded in agreement with some of these posts to further highlight the dissenting opinions.
Cue and some other execs probably saw all this snowballing, did some napkin calculations on what they were saving by zero rating royalty payments to artists, and quickly determined this was not worth taking the pain over. Tim Cook agreed (after having the numbers further scrutinised) and green lighted Cue putting out the message tonite - we are paying artists.
Right now they are probably cursing missing this detail on royalties during trial when putting together the deals. But it's not surprising the bulk of the attention was on subscriptions, foregoing revenue for 90 days. Because that's were the bulk of the money is earned and paid out.