Why and how the text could be Bavarian

[JoJo_Jost]

Oh, sorry, I misunderstood you there.

Yes, that’s also (as a possible theory) easy to explain:

Even a single hand could write the same word in very different ways. You see this time and again in manuscripts.

Typical examples of such variations:

und / vnd / vnnd / unnd  (and) 
ich / ichs / ih / i  (I)
sein / seyn / seinn (to be)
zu / ze / zů / zue (to/close)
nicht / nit / nycht / nitt (not) 
wasser / wazzer / wasser / waßer (water)

This is quite normal for Early New High German. There was no modern, fixed orthography.