The HubPages commenting system has an automatic feature that flags some comments as spam but allows you to make the final decision to allow or delete the comment. I have had some comments that were flagged that were not spam but most that are flagged automatically are spam. There is certain criteria that the HP system picks up to identify a comment as spam, usually there is a link inside the comment that directs to an outside site, and the comment is usually from a someone who is not registered on HubPages. If you want to allow the comment and you don't consider it to be spam, you may allow it to be shown.
Hope this helps!