Question on Making the Night Scene

Hello,

I'm confused why my scene isn't in complete darkness like in the tutorial. This is at 19:20 in the video.
I changed the HDRI to the night scene, changed the background strength to 1 and then disconnected it from the world output node. I also reset the exposure. I don't know what light source this is coming from. As far as I know, my setup is matching the tutorial's directions.

Thanks!