He does fall behind briefly while he stares, but he bounces back to following soon after. Even without his magic, skeletons weigh very little compared to other similarly sized creatures, and he can bound with the best of them.

"A... decorative cage?" Papyrus suggests at first, then shakes his own head. "Wait, no. The difference is simple! You can leave a wall or a house, if there's an open door. It's only a cage... if you can't leave."

He knows the difference from experience, now that he's living on the surface. The room in the barracks isn't much to look at, it's barely a home, but it is a place to stash his things and occasionally nap. The freedom with which he takes to the outdoors, directly under the sky... He wouldn't trade it for his house in Snowdin any time soon, that's for sure.