It seems more like he wrote some stuff that sounded cool , but then found he'd written himself into a corner and made up more stuff until he foudn a way out.I mean okay, but I know he figured out the sun and the moon by having light move at an incredibly slow speed. or something like that. the point is he figured some stuff out, even if it was hand wavey.
He made it so that Discworld's sun and moon were a pair of objects orbiting Great A'Tuin. But, he also described a normal sunrise, with day/night terminator. But on a flat disc, the terminator moves along at the speed of light - the entire disc would see the sun nigh instantaneously, so he wrote some florid stuff about the speed of light... which he then ignores for the rest of the work, which is good, because he'd also have issues with people looking at things at any appreciable distance. He wrote until he cold sweep the issue he'd created under the metaphorical rug.
And that's fine. For a fantasy series there's no problem with that. But it then follows - you don't actually have to figure anything out - unless it is going to be part of the plot the characters deal with, you don't need to specify how things work!