From your source:
There are some commercial vegan diets available which have synthetically made nutrients to replace those found only in animal based ingredients.
The discussion is about commercial vegan cat food, which had the nutrients cats need, just sourced without killing other animals. The science on these diets is still relatively new, but early studies are looking pretty good.
Taurine is usually singled or because it is the only nutrient required to meet the AACFO cat food guidelines that can not be readily sourced directly from plants.