Is the El Burro cheese enchilada fully vegetarian?

A while ago, I went to El Burro with family and ordered the cheese enchilada, thinking it would be vegetarian. However, after several mouthfuls I started getting a stomach ache. So I started to wonder...is the brown sauce they use fat or broth? I can't think what else would have caused a stomach ache, and I can't find what ingredients they use online.