Not sure how this guy was surprised. The vegetarian burrito there has always explicitly been black beans only, which should have been a clue. And I was a vegetarian – for no particular reason – for three years and I’ll tell you this: if you blindly believe that anything in any restaurant will be vegetarian-friendly, you’re a moron. Unless explicitly stated, assume everything has some sort of meat in it. Especially anything with beans. Restaurants always throw bacon or hog fat or pork rinds or fetal pigs or Piglets in with their beans.
If you’re wondering, Subway and Chipotle are just about the only mainstream chain restaurants where you can get something resembling a meal if you’re a vegetarian. Most Subways have the “veggie patty” (basically a Morningstar fake meat thing that’s oddly satisfying) and you can probably find enough variations in salsas to keep the vegetarian burrito at Chipotle interesting.