What to do?

So little man is 8.5 months. He can roll from his tummy to his back reliably. From back to tummy is sketchy. He's only done it a couple of times. I put him to bed tonight and go lock up the house for the night. I leave his night light on for this. When I come back this to turn his light off this is what I see. We don't have a video monitor, just audio so I don't know if he's doing this every night or not. I know when he gets up in the morning he's been on his belly but I'm not sure if he's sleeping that way or waking up and rolling over. Do I leave him be? Or risk the wrath of the baby bring woken up?