Why and how the text could be Bavarian

[JoJo_Jost]

In your opinion, was our author not only a physician knowledgeable in anatomy, a pharmacist, and a herbalist, but also an exceptional cryptographer, ahead of his time?

No, not at all; all of this fits perfectly with the cryptographic practices of the early 15th century. In fact, I tend to think it's not really a very good cipher.

And anatomical examinations of corpses were being conducted at the same time (in other Countries) - and even earlier.