I would give him time, if I were you. After a month of dating, that’s still pretty early in a relationship. Sleeping on someone else’s house can be scary, so early on.
After all, you wouldn’t want to be forced into something you’re not ready for either.
I totally get your side too, it may seem weird but it’s his boundary to set. He has said no, and no still means no.
The best thing you can do is to keep the invitation open and talk about it with him. Find out what he thinks or fears is going to happen.
Maybe he had a bedtime ritual that he’s not yet willing to share yet.
It’s white and gold!
All joking aside, most stairs that I know had some sort of overhang, which we don’t see in this picture, so I’ll venture to say that we are looking down. The mattress is at the bottom of the stairs.