Moon visible through clouds in underground cave

So I launched my game I was a little bit bored, I decided to dig a hole. This was a flat world with a couple of trees. It was miner's dream world. I dug down about 100 blocks and made a giant block shaped hole in the ground. I put the hole where it was because The ceiling would have clouds because of the flat world gen. It was amazing. I flew up high and noticed a cube shaped light in the clouds. I flew up and hit the stone ceiling of the pit. I was confused. Was this the sun? To make sure, I set the time to night. Sure enough, the moon was there. This is a pretty nice thing, Its fun to have in my world, regardless, I am reporting it because I know its a bug. In one of the pictures I am attaching it, the clouds are dark and the moon is visible, in the other, the clouds are a grayish color and sun is visible. There was no game crash.