Yes, your users aren't using your search engine as an oracle for the truth, they're using it to find pages with similar text. It's their job (and specifically not yours) to determine how well the text they find corresponds with reality. Perhaps they're even aware the site is factually incorrect and enjoy reading it for the novelty, perhaps they want to cite it to warn others that sometimes things online are wrong. You have no idea what the people are doing with the information.
Google has started censoring their results because they decided people should use their search engine as a truth oracle (with the results you would expect, lets not forget the "when did George Washington go to the moon" thing from a year or so ago.) I think that's a mistake and is a large part of the reason I use DuckDuckGo.
You may have caught this one instance but there are likely an unlimited number of others. You're not going to catch everything and you make your search engine worse with every exception you make to the algorithm.