I don't know how much the idea is accepted within the community, but for me the most probable case seems to be some guy writing half truth (real plants, constellations), half fiction (imaginary plants and mechanisms) with either made up or intentionally very unknown, even at the time of writing language, script as a hobby/work. The illustrations, even the strange ones, fit the art style of the time pretty well, and if there were people willing to buy things like that, why not make it?
Seems perfectly reasonable course of action to produce it, only thing that's strange is that there aren't more these kind of scripts. Or there are, we just haven't heard of them because they were either in known languages, or deciphered?
Seems perfectly reasonable course of action to produce it, only thing that's strange is that there aren't more these kind of scripts. Or there are, we just haven't heard of them because they were either in known languages, or deciphered?