For some vegetarians who have not had any animal protein in their bodies for years, eating somthing that was cooked in animal fat, or has chicken broth as a base can indeed make them sick. Nowhere near as sick as consuming gluten for those unable to digest it, but violent stomache cramps and the like.

I am a vegetarian and thankfully it has not happened to me, but I do know others it has happened to.

As for the *A meals, I have had veg on LH, SK, BD, UA, AC and OS - can't say as any were particularly bad, except for the purser on AC yelling at me for not eating the fish when they forgot to load my veg meal.