As the article says:
" If you're a mathematician the argument is not difficult to follow, but it's not so easy for most people. That's a pity, since the underlying reasons for universality are simple and beautiful."
Indeed, as a mathematician, the universality of neural networks is obvious to me from their definition. However, this article is explicitly not aimed at mathematicians, and (as far as I can tell) does a good job of presenting the argument without requiring unnecessary math knowledge, which is something that we tend to be bad at doing.
Furthermore, the universality does not directly follow from the quote you provide, as you would still need to show that the hidden layer neurons form a basis. Infact, the article was about constructing such a basis in the neurons. The only thing that bringing in your quote would serve to do is make the article more confusing by unnecessarily introducing the concept of basis functions.