I mentioned a few posts ago that their natural beef flavor has no beef, its plant and milk derived. Which makes them not vegan of course, but my point is that it may or may not make them vegetarian depending on the type of vegetarian they are. Its possible other compounds that go on the fries outside of the “natural beef flavor” comes from animals though, but its also possible McD’s is just outright saying their fries aren’t vegetarian friendly to avoid any issues which seems likely to me.
Edit:
As far as eating at McD’s i think i do so maybe once or twice a year. I don’t mind it, i think it’s “ok” but in general i’ve been trying to eat less junk food 
