Maybe not a bad thing, but seems less of a strong signal of “goodness” compared to a book recommended the same number of times by different users. You might consider capping the number of times you consider recommendations for one book from a single user to something reasonable, like 3. That way you get more of a crowd consensus as to what’s really good.
I don't know what changes, if any, would stop this problem from occurring. It just jumped out as a case of a book at the top of a list that doesn't really address the topic in question. It does seem like an outlier in the data, right?
Maybe, though, there's some hidden validity to the implied idea that assertiveness is a key issue in the RPG community.