And flying over the forest is hard. Stone has done a little of it, and can't seem to get enough lift to actually clear the tallest trees, not for long. So he hasn't gone far enough to even count as an exploration. Flying up towards the stars might be harder, but he's willing to give it a shot.

"We have other fliers around here, right? Aziraphale has wings, and that fluffy bird-girl. And I read that someone else can just kind of hover." None of them are Stone, but they still have them.