My email newsletter gets flagged as a "HTML:Facebook-A [Phish]" threat

Can someone please explain to me exactly what this means? My subject line is “Facebook Defamation: Truth is not Enough” and although it is coming from a 3rd party mail server, all of our DKIM and SPF records are in place… Presumably it think that the email is trying to pretend to be from facebook?

I haven’t picked up any other software that flags the email… Any suggestions?