No, we require people to create an account to post a comment. We didn't for the first 4 years or so and often had authors quit because of the abuse they suffered in the comments, and it was a fulltime job keeping the spam off the sites. Once we switched to registration both those problems ended overnight. This person can easily set up a throwaway e-mail account and then register with that which allows them to remain anonymous - we don't require real names but do hold people accountable for their own words.
Also, FYI, this topic has been covered at length on the authors forums.