Sam walked out onto the landing at the top of the stairs, leading all the way down the apartment building and heard someone call out. He was grateful that someone else was in here and alive but he knew better to call out and so didn't return the call for fear of being found by the infected. Waiting to see if any came to the call of this person,  still clutching his guitar, he quietly leaned over the railing and looked down the stairs, shining his torch down to spot anyone but only finding corpses.