If I understand your example correctly, you mean to say that wash trading can be used to inflate prices. This could be true if Tether was simply another no-name altcoin with abnormally large percentage volume on Kraken. However, Tether trades on the magnitude of a few billion USD daily[1]. $13 million is a drop in the bucket. And as the article states, the trade did not impact price.
[1] https://coinmarketcap.com/currencies/tether/