The nymphs are possibly inspired from Dante manuscripts

[Koen G]

But keep in mind that those nymphs are very small, about 20 mm tall.  It  is very hard to draw an anatomically correct human body at that scale, without first sketching it in pencil (a trick that Scribe obviously did not know).  Trained artists like Leonardo (or even Taccola) could do it.  A small-town accountant or lawyer probably could not.

One of the things I gradually realized is that things like very basic skeletal accuracy are a sign of skill, and they sit much lower on the ladder than you might think. Even in lower quality manuscripts, arms connect to shoulders, elbows work well and bulls' hind legs bend correctly.

Just for myself, I found it liberating to be able to say "this detail is probably the result of bad drawing" rather than having to find a cultural or compositional explanation for everything.

This does in no way imply that I think the drawings are meaningless. But both things can coexist: a poor artist trying to communicate something through drawings. But that something is not standard, even if we normalize for the effect of poor technique.

As for the background of the artist, one potential (of several) ideas I like is that he may have travelled as a student, as many did. When I was knee-deep in Taccola research, one of the things I learned is that he had a lot of contact with the students of the university in Siena. German (speaking) students were the largest groups of foreigners here, those who lived "above the mountains". And one of the hypotheses for the manuscript with the VM parallels is that it may have been available to students. (This is based on my recollection of an article I read at the time).

A common thread among several works we have marked as potentially relevant is their role in Italian pedagogy and education: De Balneis, La Sfera... In places like Florence, you would encounter these works at some point in the curriculum, especially when pursuing medical studies.

So, coming back to the earlier question, I believe one explanation for a diversity of influences is ironically that the person had (or was having) an education - just not one focused on illumination! I realize this point of view clashes with other popular options, like that the artist lived an isolated life or that they must have suffered from some form of mental issues.