Yeah... the article has a lot of "simplifications" that the reader has to just kind of trust the author on... and those are meant for people with not a lot of mathematical sophistication. All this talk about "shrink fast enough" and why it's important is just some intense handwaving w/o any actual explanation.
To be fair, it's kind of upsetting, but maybe there's no way to help it... some mathematical proofs can be "dumbed down" to the point that people with very little background can understand them. The proof of sqrt(2) being irrational might be one of those. But, what's given in the article feels like either the author didn't really understand the subject, or she couldn't explain what she understood in simple terms. But, it's really rare that there's such an easy to understand proof or concept. So, I don't blame her.