Your instincts are on target. Some otherwise truly wonderful dogs startle or exhibit sleep aggression. If our dogs are sleeping, it is our engrained habit to speak to them (to insure they are awake) before touching them. I think of it as a courtesy or kindness to the dog.
We've added a second Greyhound twice over the past several years and witnessed similar behavior so this sounds normal to me. How are they doing now, almost a week later? We once had a very affectionate male (a "leaner" who was quite people-oriented). He was a wonderful boy. Congratulations on your addition.