Six onion-roof towers supporting heavens

[Rafal]

What is true, however, is that the author could have come from anywhere. But the fact that there are almost no Christian symbols throughout the manuscript does not necessarily mean that the author was not a Christian. It is more likely due to non-religious themes.

I would add that he probably wasn't very religious.
We have a strong hypothesis that at the page f85r2 he mistakes rosary for some chain:
   

We don't  know the original manuscript that was his inspiration, we only know its "cousins". But a religious man would recognize a rosary no matter how imprecise it was drawn.

I would say it's a stereotype that everyone was religious in middle ages. Sure, there weren't officially declared atheists. But there were certainly people who simply didn't care, didn't go to church and didn't know religious symbolism.