I've dug around the TempleOS codebase a bit, and while it certainly is impressive for a single guy's work, I think there's been an overcorrection where people act like Terry was some hyper genius instead of "a pretty smart guy".
I kind of got the impression that whenever Terry didn't know how to do something, he would just convince himself that that's not what God wanted anyway and stop doing it.
I don't think most people actually believe he was one of the smartest people of all time or anything. He was obviously a seriously talented programmer, and impressively so: when you consider the number of humans that can program at all on earth, and then the number that can write a compiler, and a complete operating system/desktop environment/shell/games, while suffering from severe mental illness no less—you end up with a vanishingly small group.
Most of the people we think of geniuses are not smarter than the average smart person, but they persevered more. Terry had the ultimate driver of perseverance: severe mental illness.
Given that Terry described the manic episodes as "a revelation from God" I think theopneustos is an accurate description. It just means "God Breathed" or "Inspired by God"
The announcement blog post (https://blog.orhun.dev/introducing-ratty/), which would've been a better submission URL, unsurprisingly says that TempleOS was the direct inspiration of the project.