Why did the young soldier's reply send a shiver down Joey's spine?

Joey recognized the young soldier's voice.... even thought the young soldier hadn't yet recognized him.

Yes, Sergeant,’ came the reply. A reply that sent a sudden shiver of recognition through me. Quite where I had heard the voice before I did now know. I knew only that those two words sent a tremor of joy and hope and expectation through my body and warmed me from the inside out. He led me slowly across the cobbles, and I tried all the while to see his face better. But he kept just that much ahead of me so that all I could see was a neatly shaven neck and a pair of pink ears.