I just realized; has he never fallen asleep in a car or carriage? I used to sleep in the car all the time as a kid. If he did so, would he wake up in the middle of the road when he came back? Maybe not, since he didn't wake up in the middle of space. Did he just appear back in the car like nothing happened? He couldn't have done so at all, anyway, right? Nobody knew about his ability to hop between worlds. I suddenly have so many questions.
Honestly, you just don't think about it too much.
Teleportation in fiction, in general, typically has this unexplained aspect.
There is no true "stillness" or stationary frame of reference in the universe.. so ending up inside the Earth or in space implies that one
does exist in the fictional world in question, unless something like the Sun is being used as the locational reference. Excluding the speed of light.. there is only stillness/motion when being compared to another object. It's why the current accepted rules of physics is called
General Relativity.
So it just depends what is being used as a frame of reference. If
Kazuhiro Kazuhiho's "spawning" location is being set in relative to the planet.. then yes he should logically wake up on the road shall he fall asleep in a moving vehicle of some sort. Though, if it being set in relative to whatever he is sleeping directly
on.. then no.
I actually think it's more likely the latter since he can bring food in and out of the other world by setting it by his bed, which could indicate that any bed he's using serves as a temporary interdimensional medium of some sort.
Idk.. or maybe it's just a deity of some sort that's manually doing all the work of sending him between worlds and could do it either way.