Most editors don’t do fact checking, they’re checking for readability and correct spelling / grammar. My first book was about seven years later and the copyeditor printed out the PDF and annotated it with proof-reading marks for me to get back. There were technical reviewers but they were experts in the book’s subject matter. If I made a throw-away remark on a different topic, they wouldn’t correct it unless they happened to know it was nonsense.
Remember that this predated Wikipedia. Fact checking would have meant going and finding a book about reptiles. Unless you have some reason to believe the comment is false, you definitely wouldn’t bother, and even then you might not.