It's because they intend to bring accuracy back as a healer-specific mechanic, and so there will eventually be a chance for all of our healing to miss on each individual target. It means that some party members are going to die to the incoming raid-wide attack no matter how hard you try, naturally resulting in the clown fiesta many of us refer to as the high point in the healer experience at this time.

No, just kidding, it's just weird wording, like these two have said.