I get why you'd have that impression (due to his mental illness), but TermpleOS is certainly not outsider art. While unconventional in some ways (and not sharing the aims of commercial projects), it's no more a piece of outsider art than e.g. KnightOS. Its code isn't bad, the design is certainly not idiosyncratic. It has none of the "classic" traits of outsider art that other hobby projects don't. You can read its code much like that of any other kernel. And IIRC, Terry Davis has the kind of academic credentials you'd expect from someone writing an operating system, too.