Yes, definitely. But that was a choice. There are tons of smart reasons to choose to generate the list from Amazon links, and one of them appears to have been, "because we know that they can be tagged with affiliate links."
Tagging the links was a conscious decision, but I do think that the approach of looking for Amazon links provides more insight than any other domain/online store.
It's not super clear from the website whether this is something you did primarily to learn about data analysis, learn about HN's book recommendations, or to make money. Any of those is fine! But the motivation is likely to influence the outcome (even unintentionally) and it's something that could be made more clear.