Is there a particular reason you have in mind why it wouldn't be? I'm only knowledgable on the language side, and it's definitely the right script (or, as is prone to happen with non-readers, approximations of it). Given the close contact Europeans had with the Mongols, since they fought all the way to Poland, it's exactly the sort of linguistic depiction one would expect. The "pseudo text" is a rather common occurence, especially with those languages considered exotic: just think how a modern cartoonist might fake Japanese characters, or an artist might design an "Arabic" Latin typeface.