It's too bad that the other reviewers were disappointed, but my experience didn't match theirs. First of all, the restaurant doesn't claim to be vegan - it claims to be vegetarian. That being said, I asked the server if any of the food was made without eggs and milk and he pointed to quite a few things. In fact, the entire salad bar seemed to be vegan (it included a green salad, beets, a bean salad, a rice dish, and a few other salads) and a few of the mains were vegan too. Perhaps the restaurant has changed since the other people went.
When we went, it was a buffet-style arrangement. There were two options for food, the "economico," which included salads of your choice, a main, bread or tostadas, and a juice drink. The price was 38 pesos and was quite a generous portion that I couldn't quite finish. The other option was 10 pesos more (so 48) and also included soup and dessert.
We were happy, and the restaurant was very busy. Glad to see a vegetarian restaurant being so popular! The staff that helped me was patient with my stuttered Spanish and the person that I asked about vegan food was very kind.