Barking in the middle of the night?

My 4 month old male chin barked for the first time in the middle of the night. I had never heard him make the sound before so it really scared me, the high pitched squeaky and loud noises. He stopped when we turned on the light, and I sat and watched him for a while. I added more food to his bowl and he hasn't barked since but I am wondering if he is upset? Maybe I did something wrong? He should have been cool enough, plenty of water, clean bedding, the only thing i noticed is he managed to cover all of his food with hay, so I made more of it visible to him. Is this an issue? I am wondering what the barking means, since he has not made this sound and I have had him for nearly a month now. I am hoping he is not in pain or upset, but I really don't know what that was. Any comments would be appreciated! Thank you!