Almost every major website is doing the exact same thing. Here is Wired's policy on affiliate links: https://www.wired.com/2015/11/affiliate-link-policy/

They are almost assuredly added automatically so the author had no clue it was happening. I used to author a Wordpress plugin that did this for bloggers so they wouldn't need to worry about generating links through the Amazon website then going back to their Wordpress dashboard.