There are many aspects that point to the text not being completely random or clumsily written. In particular it doesn't fall into many faults you'd expect from some non-expert trying to come up with a fake text.

The age of the document can be estimated through various methods that all point to it being ~500 year old. The vellum parchment, the ink, the pictures (particularly clothes and architecture) are perfectly congruent with that.

The weirdest part is that the script has a very low number of different signs, fewer than any known language. That's about the only clue that could point to a hoax afaik.