It was, but the author can be forgiven for mixing them up. Knuth did say it originally, but Hoare repeated it (in writing), properly attributing it to Knuth. Knuth then read Hoare's quote, missed the attribution, forgot that he was the one who said it, and repeated it again in writing, mis-attributing it to Hoare.

Not totally sure.

https://ubiquity.acm.org/article.cfm?id=1513451

> Every programmer with a few years' experience or education has heard the phrase "premature optimization is the root of all evil." This famous quote by Sir Tony Hoare (popularized by Donald Knuth) has become a best practice among software engineers.