As per the FAQ, a user needs atleast 50 Reputation points in order to leave comments globally on the site - one can always comment on one's own questions and answers and answers to questions one has asked.
This means that a user needs atleast 50 Reputation points to comment on a question posted by another user. So, how can this unregistered user (PaddyinWales) leave this comment? He/She has just 1 Reputation Point.
I don't think this should be a bug (although it could be).