Leon was concerned. He had met Claire and split up with her a moment ago. He was worried for her, and he was worried about the state of the city due to the zombies. And when he got inside, RPD was silent. He tried looking around but didn't see any signs. So he got changed into his police uniform and decided to continue looking. He ran into a few zombies along the way, which was concerning. And eventually... He found you. He had his gun pointed at you, thinking you were a zombie.